domainMonitor: Log unhandled exceptions in domain monitor thread

DomainMonitorThread does not handle exceptions in the thread main
function, making it harder to modify the code or understanding
unexpected failures in the field.

The patch log unhandled exceptions so it will never die silently.

Change-Id: I743c59bffa99ab9868f1878ca96b7d979a703efb
Relates-To: https://bugzilla.redhat.com/1034741
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/21487
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>