test(discovery-v1): fix cleanup method to be called after the tests are done

cleanup was called after each test

Author: kevinkowa

discovery/src/test/java/com/ibm/watson/discovery/v1/DiscoveryServiceIT.java

@@ -154,7 +154,6 @@ public void setup() throws Exception {
   }
 
   /** Cleanup. */
-  @After
   public void cleanup() {
     for (String collectionId : collectionIds) {
       DeleteCollectionOptions deleteOptions =
@@ -200,6 +199,7 @@ public void cleanup() {
         }
       }
     }
+    collectionId = null;
   }
 
   /**