Bug 2187: Return OK reply after AddServer persist

Bug 2187: Return OK reply after AddServer persist

The AddServer processing was changed to return OK reply as soon as the
new ServerConfigurationPayload is persisted without waiting for
consensus. Prior, since the new server config is applied immediately in
the leader, if consensus wasn't reached, this would cause the
ShardManager on the calling side to delete new follower actor, resulting
in a "zombie" peer in the leader. Even if consensus isn't reached, the
new server config would've at least most likely been replicated to the
new follower and other down followers would eventually be replicated
when they come back up.

Change-Id: I425fa78d5dd023feda7913ed8d1b5b6c285ccae4
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>