Add group for testing packages

Author: mziccard

gcloud-java-core/src/main/java/com/google/gcloud/package-info.java

@@ -17,4 +17,5 @@
 /**
  * Core classes for the {@code gcloud-java} library.
  */
+
 package com.google.gcloud;

pom.xml

@@ -394,6 +394,10 @@
                     <title>Main packages</title>
                     <packages>com.google.gcloud*</packages>
                   </group>
+                  <group>
+                    <title>Test helpers packages</title>
+                    <packages>com.google.gcloud.bigquery.testing:com.google.gcloud.datastore.testing:com.google.gcloud.resourcemanager.testing:com.google.gcloud.storage.testing</packages>
+                  </group>
                   <group>
                     <title>SPI packages</title>
                     <packages>com.google.gcloud.spi</packages>