xenapi: Adding logging for migration plugin

With this change administrators will be able to examine hypervisor
logs for real-time progress of rsync operations (resizes, migrates).

Change-Id: I463b574be1021e141fe2c8380b9c07f6cd860c78
Merge "xenapi: Adding logging for migration plugin"
Merge remote-tracking branch 'm_src_repo/master' into build-temp