r/vmhost: Retry vm-autostart if libvirt is down

If the _libvirt_ daemon has not fully started by the time `vm-autostart`
runs, we want it to fail and try again shortly.  To allow this, we first
attempt to connect to the _libvirt_ socket, and if that fails, stop
immediately and try again in a second.  This way, the first few VMs
don't get skipped with the assumption that they're missing, just because
the daemon wasn't ready yet.

roles/vmhost/files/vm-autostart.sh

@@ -5,6 +5,8 @@ if [ ! -r /etc/vm-autostart ]; then
     exit 0
 fi
 
+virsh connect || exit
+
 while read name args; do
     if [ "${name}" = delay ]; then
         sleep ${args}