Adds Instance UUID to rsync debug logging

This commit adds the instance uuid to the rsync debug output in
the debug logs. The issue we were seeing is that when multiple
migrations are ongoing at the same time, it's not easy to
track the rsync progress of each migration.
Fixes: bug #1215629

Change-Id: Iec662bdc0aed1c6f54ecaa062335dc5504ac030f

plugins/xenserver/xenapi/etc/xapi.d/plugins/migration

@@ -55,7 +55,7 @@ def _rsync_vhds(instance_uuid, host, staging_path, user="root"):
         rsync_progress = rsync_proc.stdout.readline()
         if not rsync_progress:
             break
-        logging.debug(rsync_progress)
+        logging.debug("[%s] %s" % (instance_uuid, rsync_progress))
 
     utils.finish_subprocess(rsync_proc, rsync_cmd)