Make module output more consistent wrt. changed/failed

- Make sure exit_json() always returns a changed= value
- Modify the yum module to not return failed=False
- Modify install() and latest() similar to remove() in yum module
- Changed exit_json(failed=True, **res) into a fail_json(**res)
- Make sure yum rc= value reflects loop (similar to how we fixed remove())

lib/ansible/module_common.py

@@ -594,6 +594,8 @@ class AnsibleModule(object):
     def exit_json(self, **kwargs):
         ''' return from the module, without error '''
         self.add_path_info(kwargs)
+        if not kwargs.has_key('changed'):
+            kwargs['changed'] = False
         print self.jsonify(kwargs)
         sys.exit(0)