core: remove job with migration step on engine startup

In I5973c we removed jobs that cannot be tracked after engine restart.
Proper handling for internal migration which is represented as a step
was missing, so it is added in this patch.

Change-Id: If2de0753cf2773b84a3933f8d1b22516b236ee9b
Bug-Url: https://bugzilla.redhat.com/1040952
Signed-off-by: Arik Hadas <ahadas@redhat.com>