Enable testTransactionWithIsolatedLeader() with ClientBackedDataStore

java.lang.AssertionError: unexpected exception type thrown; expected:<java.util.concurrent.ExecutionException> but was:<java.util.concurrent.TimeoutException>
	at org.junit.Assert.assertThrows(Assert.java:1020)
	at org.junit.Assert.assertThrows(Assert.java:981)
	at org.opendaylight.controller.cluster.datastore.DistributedDataStoreRemotingIntegrationTest.testTransactionWithIsolatedLeader(DistributedDataStoreRemotingIntegrationTest.java:1110)
Caused by: java.util.concurrent.TimeoutException: Waited 12 seconds (plus 217770 nanoseconds delay) for SettableFuture@654b899f[status=PENDING]
	at com.google.common.util.concurrent.AbstractFuture.get(AbstractFuture.java:508)
	at com.google.common.util.concurrent.AbstractFuture$TrustedFuture.get(AbstractFuture.java:111)
	at org.opendaylight.controller.cluster.datastore.IntegrationTestKit.doCommit(IntegrationTestKit.java:359)
	at org.opendaylight.controller.cluster.datastore.DistributedDataStoreRemotingIntegrationTest.lambda$13(DistributedDataStoreRemotingIntegrationTest.java:1111)
	at org.junit.Assert.assertThrows(Assert.java:1001)