11. core: Adding the ability to get async tasks by entity id

The following patch adds the ability to get asyncs by
entity Id

http://www.ovirt.org/Features/AsyncTaskManagerChanges_3.3
Change-Id: Id7609857273bf8ac74557ba88550dee8316eb5c7
Signed-off-by: Yair Zaslavsky <yzaslavs@redhat.com>