Clean up RedisLockRegistryLeaderInitiatorTests

Related to https://build.spring.io/browse/INT-MASTERSPRING40-1129

When there is no other candidates in the cluster, the current `yield()`
will give a leadership to the current active initiator back
Therefore a `revoke()` might not be called at all

* Fir the `RedisLockRegistryLeaderInitiatorTests` to check revoking
after `stop()` instead of `yield()`

Author: artembilan

spring-integration-redis/src/test/java/org/springframework/integration/redis/leader/RedisLockRegistryLeaderInitiatorTests.java

@@ -129,12 +129,10 @@ public void testDistributedLeaderElection() throws Exception {
 		initiator1.setLeaderEventPublisher(new CountingPublisher(new CountDownLatch(1), revoked11,
 				new CountDownLatch(1)));
 
-		initiator1.getContext().yield();
+		initiator1.stop();
 
 		assertThat(revoked11.await(60, TimeUnit.SECONDS)).isTrue();
 		assertThat(initiator1.getContext().isLeader()).isFalse();
-
-		initiator1.stop();
 	}
 
 	private static class CountingPublisher implements LeaderEventPublisher {