Havana: Fixtures: fix keystone branch name

Solve issue: « fatal: ambiguous argument 'stable/havana': unknown
revision or path not in the working tree. »

Change-Id: If4a484010e4f8a3fd8aa6f0f5434943194637331

.fixtures.yml

@@ -3,13 +3,13 @@ fixtures:
     'inifile': 'git://github.com/puppetlabs/puppetlabs-inifile'
     'keystone':
       repo: 'git://github.com/stackforge/puppet-keystone.git'
-      ref: 'stable/havana'
+      ref: 'origin/stable/havana'
     'mysql':
       repo: 'git://github.com/puppetlabs/puppetlabs-mysql.git'
       ref:  'origin/0.x'
     'nova':
       repo: 'git://github.com/stackforge/puppet-nova.git'
-      ref: 'stable/havana'
+      ref: 'origin/stable/havana'
     'stdlib': 'git://github.com/puppetlabs/puppetlabs-stdlib.git'
   symlinks:
     'ceilometer': "#{source_dir}"