Bug 4823: Use tx commit timeout for BatchedModifications

When sending BatchedModifications messages to the shard we use the
general operation timeout which is 5 sec. We should instead use the
transaction commit timeout to be consistent with the other transaction
messages (ReadyLocalTransaction, CanCommitTransaction etc).

Change-Id: I26bead59c29ee198f677838c5adb3614e3795a04
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>