bug#30728: guix-install.sh doesn't work if run with "sudo"

[Clément Lassieur]

Hi,

My system is Ubuntu 16.04.

I ran './guix-install.sh' and got the message: "This script must be run
as root.".  So I ran 'sudo ./guix-install.sh' and got an error message
saying that:

    GUIX_PROFILE="${HOME}/.guix-profile"
    source "${GUIX_PROFILE}/etc/profile"

the 'source' command doesn't work because ${GUIX_PROFILE} was never
created, ${HOME} being /home/clement, not /root.

To recover from this I had to manually delete /var/guix and /gnu, log as
root with 'su', and start again.

Clément