If the hostname of the current virtualization machine
could not be resolved, then libvirtd would fail to
start. However, for disconnected operation (on a laptop,
for instance) the hostname may very legitimately not
be resolvable. This patch makes it so that if we can't
resolve the hostname, avahi doesn't fail, it just uses
a less useful MDNS string.
Signed-off-by: Chris Lalancette <clalance@redhat.com>