************************************************************
     *                    IMPORTANT NOTICE
     *
     * When reporting bugs, include the COMPLETE, UNEDITED
     * output below in your bug report.
     *
     ************************************************************
LIBGUESTFS_HV=/home/rjones/d/qemu/x86_64-softmmu/qemu-system-x86_64
PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/home/rjones/.local/bin:/home/rjones/bin
SELinux: Enforcing
guestfs_get_append: (null)
guestfs_get_autosync: 1
guestfs_get_backend: libvirt
guestfs_get_backend_settings: []
guestfs_get_cachedir: /var/tmp
guestfs_get_direct: 0
guestfs_get_hv: /home/rjones/d/qemu/x86_64-softmmu/qemu-system-x86_64
guestfs_get_memsize: 500
guestfs_get_network: 0
guestfs_get_path: /usr/lib64/guestfs
guestfs_get_pgroup: 0
guestfs_get_program: libguestfs-test-tool
guestfs_get_recovery_proc: 1
guestfs_get_selinux: 0
guestfs_get_smp: 1
guestfs_get_tmpdir: /tmp
guestfs_get_trace: 0
guestfs_get_verbose: 1
host_cpu: x86_64
Launching appliance, timeout set to 600 seconds.
libguestfs: launch: program=libguestfs-test-tool
libguestfs: launch: version=1.25.44fedora=21,release=1.fc21,libvirt
libguestfs: launch: backend registered: unix
libguestfs: launch: backend registered: uml
libguestfs: launch: backend registered: libvirt
libguestfs: launch: backend registered: direct
libguestfs: launch: backend=libvirt
libguestfs: launch: tmpdir=/tmp/libguestfsKgILEw
libguestfs: launch: umask=0002
libguestfs: launch: euid=1000
libguestfs: libvirt version = 1001003 (1.1.3)
libguestfs: guest random name = guestfs-194p50rg5rpq1l6z
libguestfs: [00000ms] connect to libvirt
libguestfs: opening libvirt handle: URI = qemu:///session, auth = default+wrapper, flags = 0
libguestfs: successfully opened libvirt handle: conn = 0x7f780fc31f50
libguestfs: qemu version (reported by libvirt) = 1007000 (1.7.0)
libguestfs: [01629ms] get libvirt capabilities
libguestfs: [01633ms] parsing capabilities XML
libguestfs: [01634ms] build appliance
libguestfs: [01634ms] begin building supermin appliance
libguestfs: [01634ms] run supermin
libguestfs: command: run: /usr/bin/supermin
libguestfs: command: run: \ --build
libguestfs: command: run: \ --verbose
libguestfs: command: run: \ --if-newer
libguestfs: command: run: \ --lock /var/tmp/.guestfs-1000/lock
libguestfs: command: run: \ --copy-kernel
libguestfs: command: run: \ -f ext2
libguestfs: command: run: \ --host-cpu x86_64
libguestfs: command: run: \ /usr/lib64/guestfs/supermin.d
libguestfs: command: run: \ -o /var/tmp/.guestfs-1000/appliance.d
supermin: version: 5.1.4
supermin: package handler: fedora/rpm
supermin: acquiring lock on /var/tmp/.guestfs-1000/lock
supermin: if-newer: output does not need rebuilding
libguestfs: [01639ms] finished building supermin appliance
libguestfs: command: run: qemu-img
libguestfs: command: run: \ create
libguestfs: command: run: \ -f qcow2
libguestfs: command: run: \ -o backing_file=/var/tmp/.guestfs-1000/appliance.d/root,backing_fmt=raw
libguestfs: command: run: \ /tmp/libguestfsKgILEw/overlay2
Formatting '/tmp/libguestfsKgILEw/overlay2', fmt=qcow2 size=4294967296 backing_file='/var/tmp/.guestfs-1000/appliance.d/root' backing_fmt='raw' encryption=off cluster_size=65536 lazy_refcounts=off 
libguestfs: [02148ms] create libvirt XML
libguestfs: libvirt XML:\n<?xml version="1.0"?>\n<domain type="kvm" xmlns:qemu="http://libvirt.org/schemas/domain/qemu/1.0">\n  <name>guestfs-194p50rg5rpq1l6z</name>\n  <memory unit="MiB">500</memory>\n  <currentMemory unit="MiB">500</currentMemory>\n  <cpu mode="host-passthrough">\n    <model fallback="allow"/>\n  </cpu>\n  <vcpu>1</vcpu>\n  <clock offset="utc">\n    <timer name="rtc" tickpolicy="catchup"/>\n    <timer name="pit" tickpolicy="delay"/>\n    <timer name="hpet" present="no"/>\n  </clock>\n  <os>\n    <type>hvm</type>\n    <kernel>/var/tmp/.guestfs-1000/appliance.d/kernel</kernel>\n    <initrd>/var/tmp/.guestfs-1000/appliance.d/initrd</initrd>\n    <cmdline>panic=1 console=ttyS0 udevtimeout=600 no_timer_check acpi=off printk.time=1 cgroup_disable=memory root=/dev/sdb selinux=0 guestfs_verbose=1 TERM=xterm-256color</cmdline>\n  </os>\n  <seclabel type="none"/>\n  <on_reboot>destroy</on_reboot>\n  <devices>\n    <emulator>/home/rjones/d/qemu/x86_64-softmmu/qemu-system-x86_64</emulator>\n    <controller type="scsi" index="0" model="virtio-scsi"/>\n    <disk device="disk" type="file">\n      <source file="/tmp/libguestfsKgILEw/scratch.1"/>\n      <target dev="sda" bus="scsi"/>\n      <driver name="qemu" type="raw" cache="unsafe"/>\n      <address type="drive" controller="0" bus="0" target="0" unit="0"/>\n    </disk>\n    <disk type="file" device="disk">\n      <source file="/tmp/libguestfsKgILEw/overlay2"/>\n      <target dev="sdb" bus="scsi"/>\n      <driver name="qemu" type="qcow2" cache="unsafe"/>\n      <address type="drive" controller="0" bus="0" target="1" unit="0"/>\n      <shareable/>\n    </disk>\n    <serial type="unix">\n      <source mode="connect" path="/tmp/libguestfsKgILEw/console.sock"/>\n      <target port="0"/>\n    </serial>\n    <channel type="unix">\n      <source mode="connect" path="/tmp/libguestfsKgILEw/guestfsd.sock"/>\n      <target type="virtio" name="org.libguestfs.channel.0"/>\n    </channel>\n  </devices>\n  <qemu:commandline>\n    <qemu:env name="TMPDIR" value="/var/tmp"/>\n  </qemu:commandline>\n</domain>\n
libguestfs: command: run: ls
libguestfs: command: run: \ -a
libguestfs: command: run: \ -l
libguestfs: command: run: \ -Z /var/tmp/.guestfs-1000
libguestfs: drwxr-xr-x. rjones rjones unconfined_u:object_r:user_tmp_t:s0 .
libguestfs: drwxrwxrwt. root   root   system_u:object_r:tmp_t:s0       ..
libguestfs: drwxr-xr-x. rjones rjones unconfined_u:object_r:user_tmp_t:s0 appliance.d
libguestfs: -rwxr-xr-x. rjones rjones unconfined_u:object_r:user_tmp_t:s0 checksum
libguestfs: -rw-r--r--. rjones rjones system_u:object_r:virt_content_t:s0 initrd
libguestfs: -rw-r--r--. rjones rjones system_u:object_r:virt_content_t:s0 initrd.4942
libguestfs: -rw-r--r--. rjones rjones system_u:object_r:virt_content_t:s0 kernel
libguestfs: -rw-r--r--. rjones rjones system_u:object_r:virt_content_t:s0 kernel.4942
libguestfs: -rw-r--r--. rjones rjones unconfined_u:object_r:user_tmp_t:s0 lock
libguestfs: -rw-r--r--. rjones rjones system_u:object_r:virt_content_t:s0 root
libguestfs: -rw-r--r--. rjones rjones system_u:object_r:virt_content_t:s0 root.4942
libguestfs: command: run: ls
libguestfs: command: run: \ -a
libguestfs: command: run: \ -l
libguestfs: command: run: \ -Z /tmp/libguestfsKgILEw
libguestfs: drwxr-xr-x. rjones rjones unconfined_u:object_r:user_tmp_t:s0 .
libguestfs: drwxrwxrwt. root   root   system_u:object_r:tmp_t:s0       ..
libguestfs: srwxrwxr-x. rjones rjones unconfined_u:object_r:user_tmp_t:s0 console.sock
libguestfs: srwxrwxr-x. rjones rjones unconfined_u:object_r:user_tmp_t:s0 guestfsd.sock
libguestfs: -rw-r--r--. rjones rjones unconfined_u:object_r:user_tmp_t:s0 overlay2
libguestfs: -rw-rw-r--. rjones rjones unconfined_u:object_r:user_tmp_t:s0 scratch.1
libguestfs: -rwxrwxr-x. rjones rjones unconfined_u:object_r:user_tmp_t:s0 umask-check
libguestfs: [02154ms] launch libvirt guest
libguestfs: error: could not create appliance through libvirt.

Try running qemu directly without libvirt using this environment variable:
export LIBGUESTFS_BACKEND=direct

Original error from libvirt: internal error: process exited while connecting to monitor: hw/char/virtio-console.c:132:virtconsole_realize: Object 0x7f85482fb8a0 is not an instance of type virtconsole
 [code=1 domain=10]
libguestfs-test-tool: failed to launch appliance
libguestfs: closing guestfs handle 0x7f780fc31840 (state 0)
libguestfs: command: run: rm
libguestfs: command: run: \ -rf /tmp/libguestfsKgILEw