Add RaftActor integration tests

Add RaftActor integration tests

Added 2 integration tests classes,
ReplicationAndSnapshotsIntegrationTest and
ReplicationAndSnapshotsWithLaggingFollowerIntegrationTest, with tests
for various replication and snapshotting scenarios. These differ from the
RaftActorTest and behavior tests in that it uses real leaders and followers
with real RaftActors end-to-end.

Change-Id: Idfb4fbea20567cf8d86c36ed9def588261299bdb
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>