Bug 5153: Add timestamp to TransactionIdentifier

TransactionIdentifiers are created locally but sent to the remote leader
so it's possible, after a restart, for the remote leader to see the same id
for 2 different txns since the local counter starts at 1. To alleviate
this I added a timestamp to TransactionIdentifier. I could've just used
a UUID but the counter is useful for debugging and a full UUID would
make the string version pretty long for logging. I think an additional
millisec timestamp is sufficient.

Change-Id: Iaabd3d25eb64dd14053f96336c48de90d4364678
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>