Handle leader change on ForwardedReadyTransaction in Shard

Handle leader change on ForwardedReadyTransaction in Shard

When the ShardWriteTransaction actor sends the ForwardedReadyTransaction
to the Shard, if the local shard is no longer the leader it still tries
to commit the transaction. Replication fails and it ends up timing out
but a side effect is that it persista a new log entry which isn't good.

Therefore I added logic similar as was done with ReadyLocalTransaction
to forward to the leader. For ReadyLocalTransaction, a special
serializer was added to marshal it over the wire as a BatchedModifications
message. Rather then creating another serializer, I converted the
ForwardedReadyTransaction instance to a ReadyLocalTransaction instance.

Change-Id: Ia44e86606846f2af9599ad222b7dcae1bd0cf804
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>