Fix keyerror with synchronize

Apparently we may need to initialize the option if it isn't present.

Change-Id: I4a9f4f2ace3aeb914feba868e2ac8a86223232be
diff --git a/zuul/ansible/action/synchronize.py b/zuul/ansible/action/synchronize.py
index 88ca13a..fa3d051 100644
--- a/zuul/ansible/action/synchronize.py
+++ b/zuul/ansible/action/synchronize.py
@@ -26,6 +26,8 @@
         dest = self._task.args.get('dest', None)
         pull = self._task.args.get('pull', False)
 
+        if 'rsync_opts' not in self._task.args:
+            self._task.args['rsync_opts'] = []
         if '--safe-links' not in self._task.args['rsync_opts']:
             self._task.args['rsync_opts'].append('--safe-links')