The restore snapshot is supplied by the derived actor's
RaftActorRecoveryCohort. If one exists the the RaftActorRecoverySupport
desrializes and applies the snapshot.
I also add a Builder to MockRaftActor to make it easier to pass
additional params.
Change-Id: Ib52b24331038ed48221cc27086fa3cceafe39fcf Signed-off-by: Tom Pantelis <tpanteli@brocade.com>