Fix intermittent failure in testLeadershipTransferOnShutdown

Fix intermittent failure in testLeadershipTransferOnShutdown

10:03:06 java.util.concurrent.ExecutionException: ReadFailedException{message=Error executeRead ReadData for path /(urn:opendaylight:params:xml:ns:yang:controller:md:sal:dom:store:test:cars?revision=2014-03-13)cars/car, errorList=[RpcError [message=Error executeRead ReadData for path /(urn:opendaylight:params:xml:ns:yang:controller:md:sal:dom:store:test:cars?revision=2014-03-13)cars/car, severity=ERROR, errorType=APPLICATION, tag=operation-failed, applicationTag=null, info=null, cause=org.opendaylight.controller.md.sal.common.api.data.DataStoreUnavailableException: Shard member-2-shard-cars-testLeadershipTransferOnShutdown currently has no leader. Try again later.]]}
10:03:06 	at org.opendaylight.yangtools.util.concurrent.MappingCheckedFuture.wrapInExecutionException(MappingCheckedFuture.java:64)
10:03:06 	at org.opendaylight.yangtools.util.concurrent.MappingCheckedFuture.get(MappingCheckedFuture.java:92)
10:03:06 	at org.opendaylight.controller.cluster.datastore.DistributedDataStoreRemotingIntegrationTest.verifyCars(DistributedDataStoreRemotingIntegrationTest.java:215)
10:03:06 	at org.opendaylight.controller.cluster.datastore.DistributedDataStoreRemotingIntegrationTest.testLeadershipTransferOnShutdown(DistributedDataStoreRemotingIntegrationTest.java:928)

From the logs it seems member-2 hadn't gotten MemberUp for member-3 after the
leader transfer and by the time it tried to read. I added calls to wait for members
to be up. After the change it ran 333 times w/o failure.

Change-Id: Ifbbf304230292f69429d3086867679effb8db01c
Signed-off-by: Tom Pantelis <tompantelis@gmail.com>