bug#23811: shepherd: tests/respawn-throttling.sh fails sporadically

[Mark H Weaver]

On core-updates, both shepherd and dmd failed on i686 and armhf in the
same test:

tests/respawn-throttling.sh in shepherd:

  http://hydra.gnu.org/build/1241860 (shepherd-i686)
  http://hydra.gnu.org/build/1246005 (shepherd-armhf)

and tests/respawn.sh in dmd:

  http://hydra.gnu.org/build/1245596 (dmd-i686)
  http://hydra.gnu.org/build/1248237 (dmd-armhf)

This has been happening for a long time, and although it happens more
frequently on i686 and armhf, I've archived failure logs from hydra for
the same failures on mips64el in both shepherd and dmd, and it also
happened at least once with dmd on x86_64.  I can provide these logs if
requested.

      Mark