Forward pending transactions on leadership change

If the current leader is deposed for some reason and it has pending
tx's, on leader change, the tx's will now be converted to
BatchedModifications messages and forwarded to the new leader in the
ready state so the new leader can complete the commits. Previously
they were aborted and failed.

In addition, if there's a current transaction that had already been
canCommitted and possibly preCommitted, CanCommitTransaction and
CommitTransaction messages will also be sent to the new leader appropriately.

Change-Id: I9bbd68856586c15464f4ca0e844f040c6bb5f30a
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>