Always add release tag to travis build images

Author: LPowlett

.travis.yml

@@ -28,8 +28,8 @@ env:
     - MAIN_BRANCH=private-master
     - MQ_LTS_VERSION=9.2.0.1
     - TAGCACHE_FILE=tagcache
-    - RELEASE=
-    - RELEASE_LTS=
+    - RELEASE=r2
+    - RELEASE_LTS=r1
 
 go_import_path: "github.com/ibm-messaging/mq-container"