[TEST] Increase timeout for awaiting alias & document creation

Test waits 10 seconds for all 10 aliases and documents to be created,
but it can take longer that that on slower machines.

core/src/test/java/org/elasticsearch/aliases/IndexAliasesIT.java

@@ -477,7 +477,7 @@ public class IndexAliasesIT extends ESIntegTestCase {
             });
         }
         executor.shutdown();
-        boolean done = executor.awaitTermination(10, TimeUnit.SECONDS);
+        boolean done = executor.awaitTermination(20, TimeUnit.SECONDS);
         assertThat(done, equalTo(true));
         if (!done) {
             executor.shutdownNow();