unix: Don't fail on FreeBSD running ZFS (#461)

• unix: Don't fail on FreeBSD running ZFS

ZFS doesn't support posix_fallocate() so libqb IPC or RB would
always fail with EINVAL.

As there seems to be no prospect of a more useful return code,
trap it in a QB_BSD #ifdef. That way if we do have actual errors
in the posix_fallocate() call the Linux tests should still find them.

Also, stick a small sleep in the test_ipc_disconnect_after_created
test to allow the server to shutdown before killing it with SIGTERM
and causing a test failure. all the other uses of it seem to have this
sleep!