core: task list in Webadmin - jobs disappear while still running

Previous commit deleted jobs that had at least one step that doesn't
have an async task. Proper logic is to delete jobs that doesn't have
steps with async tasks.

Change-Id: I772ec5a6255351cd3145295c783385bf0a0c4de0
Bug-Url: https://bugzilla.redhat.com/1064227
Signed-off-by: Oved Ourfali <oourfali@redhat.com>