Remove ClusterImpl#isShutdown method (#373)

Author: sashapolo

cluster-api/src/main/java/io/scalecube/cluster/Cluster.java

@@ -141,11 +141,4 @@ public interface Cluster {
    * @return promise which is completed once graceful shutdown is finished.
    */
   Mono<Void> onShutdown();
-
-  /**
-   * Check if cluster instance has been shut down.
-   *
-   * @return returns true if cluster instance has been shut down; false otherwise.
-   */
-  boolean isShutdown();
 }

cluster/src/main/java/io/scalecube/cluster/ClusterImpl.java

@@ -558,11 +558,6 @@ public Mono<Void> onShutdown() {
     return onShutdown.asMono();
   }
 
-  @Override
-  public boolean isShutdown() {
-    return onShutdown.asMono().toFuture().isDone();
-  }
-
   private static class SenderAwareTransport implements Transport {
 
     private final Transport transport;

cluster/src/test/java/io/scalecube/cluster/ClusterTest.java

@@ -471,7 +471,6 @@ public void onMembershipEvent(MembershipEvent event) {
 
     node2.shutdown();
     node2.onShutdown().block(TIMEOUT);
-    assertTrue(node2.isShutdown());
 
     assertTrue(leavingLatch.await(TIMEOUT.getSeconds(), TimeUnit.SECONDS));
     assertTrue(removedLatch.await(TIMEOUT.getSeconds(), TimeUnit.SECONDS));