Prepare the final stable/train release

The stable/train is entering in extended manitenance. Because we have
seveal changes merged since the last release, a new release should be
created before that.

Change-Id: I8a3fc453703a3ec17ebc58851c38441460f0aaf9

metadata.json

@@ -65,5 +65,5 @@
     ],
     "source": "git://github.com/openstack/puppet-openstacklib.git",
     "summary": "Puppet OpenStack Libraries",
-    "version": "15.4.0"
+    "version": "15.5.0"
 }