Fix forwarding in Shard.handleBatchedModifications
Addressed the TODO in Shard.handleBatchedModifications to handle the
case where the BatchedModifications is not the first batch when leadership
changes and the BatchedModifications needs to be forwarded to the new
leader. Added code in ShardCommitCoordinator to reconstruct all previous
BatchedModifications messages, if needed, from the transaction
DataTreeModification, honoring the max batched modification count.
Change-Id: I4fecb71be91aee24072086e1565437a69c20c8d9
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>