Fix LeaderInitiatorTests race condition

https://build.spring.io/browse/INTEXT-SIH1-10

When `LeaderInitiator` yields its leadership there is a good chance that it will obtain it back, so there is no guaranty that it isn't leader after revoking

spring-integration-hazelcast/src/test/java/org/springframework/integration/hazelcast/leader/LeaderInitiatorTests.java

@@ -166,7 +166,6 @@ public class LeaderInitiatorTests {
 		initiator1.getContext().yield();
 
 		assertThat(revoked11.await(10, TimeUnit.SECONDS), is(true));
-		assertThat(initiator1.getContext().isLeader(), is(false));
 
 		initiator1.destroy();
 	}