Bug 2187: Implement add-shard-replica RPC
The unit test creates 3 actor systems each with their own datastores.
Now that the ShardManager persists shard info and due to the static
nature of the InMemorySnapshotStore, each ShardManager needs to have a
unique persistenceId otherwise the equivalent ShardManager's persistence
Ids will clash. Therefore I added a shardManagerPersistenceId field to
the DatastoreContext so the unit test can provide a uniique Id based on
member name.
Change-Id: I907cd568d64f43586ffc1ec8581e4208f46db327
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>