agent: use vdsm domain monitor

Ensure that the storage domain is monitored by VDSM using the
repoStats and startMonitoringDomain APIs.

Change-Id: I9bab369784fecbf972622922a925fd0b45de123f
Requires: http://gerrit.ovirt.org/19762
Requires: http://gerrit.ovirt.org/20099
Bug-Url: https://bugzilla.redhat.com/1017406
Signed-off-by: Greg Padgett <gpadgett@redhat.com>