sp: add logging for stale domain link collection

This patch adds logging to the stale domain link collection in order to
better track links life-cycle.

Related-To: https://bugzilla.redhat.com/show_bug.cgi?id=1116585
Change-Id: Ia0aabbf62ab347e34e9d4efe922ea95d33290ef6
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/30246
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Allon Mureinik <amureini@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>