[TEST] make sure update task is actually executed

The update task that was submitted in this test never got executed
if node_2 was not master.

src/test/java/org/elasticsearch/indices/store/IndicesStoreIntegrationTests.java

@@ -154,6 +154,10 @@ public ClusterState execute(ClusterState currentState) throws Exception {
                         .build();
             }
 
+            public boolean runOnlyOnMaster() {
+                return false;
+            }
+
             @Override
             public void onFailure(String source, Throwable t) {
             }