vdsm: Fix check for connection issues with libvirt

There has been a made a mistake by mixing domain codes
with error codes of libvirt.
Additionally libvirt is reporting VIR_ERR_INTERNAL_ERROR
if libvirtd gets restarted or stopped somehow (e.g. after a crash)
This fix takes care to cleanup the mixup and adds the missing
error code.

Change-Id: I051d007529e22b0c4ca703042ce1601b4b2817e0
Signed-off-by: Vinzenz Feenstra <vfeenstr@redhat.com>
Bug-Url: https://bugzilla.redhat.com/852956
Reviewed-on: http://gerrit.ovirt.org/13990
Reviewed-by: Saggi Mizrahi <smizrahi@redhat.com>
Reviewed-by: Michal Skrivanek <michal.skrivanek@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>