BUG-7033: Remove payload replication short-circuits
Removed the code paths in ShardDataTree#startCommit whereby it
short-circuits the call to persistPayload. This simplifies the
code in ShardDataTree. For UNMODIFIED DataTreeCandidates we still
want to replicate so followers have an accurate view of transaction
states. For the case where persistence is disabled and there are no
followers, I modified persistPayload to check those conditions and
short-circuit.
Change-Id: Ifb940f950b076b5f9cedd91c42d3e065db92a7c5
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>