engine : Tunnel calls to AsyncTaskManager and introduce CoCo

All calls to AsyncTaskManager are made through TaskManagerUtil.
This lets us move the code around without effecting other classes.

CreateTask, CreateConcreteTask, CancelTask and RevertTask have
been moved to CommandCoordinator, a new class. Which just has these
four functions for now.

Change-Id: Ic075b65ebc2dcd067c3fe514fe03dbb719b54e94
Bug-Url: https://bugzilla.redhat.com/1083769
Signed-off-by: Ravi Nori <rnori@redhat.com>