The parameter is reported by virDomainGetJobStats API and
VIR_DOMAIN_EVENT_ID_JOB_COMPLETED event and it can be used to identify
the operation (migration, snapshot, ...) to which the reported
statistics belong.
https://bugzilla.redhat.com/show_bug.cgi?id=1441563
Signed-off-by: Jiri Denemark <jdenemar@redhat.com>