Refactor publisher.sls and server/init.sls to support registry variable

Change-Id: I782eb9fdb2439f058d7fdc94a9d07f0873d1ef9a
diff --git a/aptly/server/init.sls b/aptly/server/init.sls
index a148959..632ea45 100644
--- a/aptly/server/init.sls
+++ b/aptly/server/init.sls
@@ -29,7 +29,7 @@
     - source: salt://aptly/files/aptly
     - template: jinja
     - defaults:
-        image: {{ server.source.image|default('tcpcloud/aptly') }}
+        image: {{ server.source.registry + "/" if server.source.registry is defined else "" }}{{ server.source.image|default('tcpcloud/aptly') }}
         aptly_home: {{ server.home_dir }}
         aptly_root: {{ server.root_dir }}
     - mode: 755