cast/copy keys() to list to avoid py3 errors

In py3, dict.keys() is a view and not a copy of the
dicts keys, so attempting to delete items from the dict
while iterating over the keys results int

RuntimeError: dictionary changed size during iteration

Resolve by casting .keys() to a list() type.

(cherry picked from commit 2addc09050)

lib/ansible/plugins/action/synchronize.py

@@ -114,7 +114,7 @@ class ActionModule(ActionBase):
         # connection to the remote host
         if 'ansible_syslog_facility' in task_vars:
             del task_vars['ansible_syslog_facility']
-        for key in task_vars.keys():
+        for key in list(task_vars.keys()):
             if key.startswith("ansible_") and key.endswith("_interpreter"):
                 del task_vars[key]