engine : Introduction of CallBack interface

CallBack interface with endAction method has been
introduced. This reduces the depency of AsyncTaskManager
on bll.

Change-Id: I8c12315c96168fd32dc05ac6de336ccdd63c9fbc
Bug-Url: https://bugzilla.redhat.com/1083769
Signed-off-by: Ravi Nori <rnori@redhat.com>