Fix shard commit deadlock

Fix shard commit deadlock

When performing coordinated commits we need to ensure transactions
hit all shards in the same order as otherwise we could end up
with an ABBA deadlock -- which gets resolved through commits timing
out, but nevertheless it imposes a dealy of up to 30 seconds.

Make sure we always send entries to shards in the same order and
also synchronize all TransactionProxy instances so that transactions
have a total order.

JIRA: CONTROLLER-1833
Change-Id: Ia3076efde1c7cb5f115305593776ffa7422e7a09
Signed-off-by: Tom Pantelis <tompantelis@gmail.com>