Fixed concurrency bug in DOMTransactionChainTest

Delete transaction was commited before read was verified
since transaction commit was done in other thread
there was race-condition between allocating transactions
to verify datastore state.

Change-Id: I1717efbe160e59f42c3baca2f5a5f053d703350e
Signed-off-by: Tony Tkacik <ttkacik@cisco.com>
Merge "Fixed concurrency bug in DOMTransactionChainTest"