container_startup_config: remove old startup config files

These files aren't needed anymore, since we generate one JSON per
container in its step directory.
We now make sure these files don't exist so there is no confusion.

Change-Id: I9674102d6b3686206eec78f8d6f4408988a69b7b
(cherry picked from commit 1f3ecf2a85)

tripleo_ansible/ansible_plugins/modules/container_startup_config.py

@@ -16,6 +16,7 @@
 #    under the License.
 __metaclass__ = type
 
+import glob
 import json
 import os
 import shutil
@@ -122,9 +123,13 @@ class ContainerStartupManager:
         self.results['changed'] = True
 
     def _cleanup_old_configs(self):
-        """Cleanup old container configurations and directories.
+        """Cleanup old container configurations from previous releases.
         """
-        # TODO(emilien) remove old .json in /var/lib/tripleo-config/*.json
+        pattern = '*docker-container-startup-config*.json'
+        old_configs = glob.glob(os.path.join('/var/lib/tripleo-config',
+                                             pattern))
+        for config in old_configs:
+            os.remove(config)
 
 
 def main():