Add getOwnershipState method to EntityOwnershipService

Add getOwnershipState method to EntityOwnershipService

Added a new method to gte the current ownership state for an entity.
This was requested for OF clustering.

The DistributedEntityOwnershipService obtains the EntityOwnershipShard's
DataTree via a new message GetShardDataTree and reads the entity's owner
leaf in order to build the resulting EntityOwnershipState. The DataTree
is obtained once and cached.

Change-Id: Ib4aa2f4e5370d8d5183908b836417936a51458f7
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>
(cherry picked from commit dd6976c24f12c7cef7bed8fa6bc645dc699dda4f)