Description of problem:
rgw: change loglevel to 20 for 'System already converted' message

Upstream tracker: http://tracker.ceph.com/issues/18919


Version-Release number of selected component (if applicable):
Red Hat Ceph Storage 2.1
10.2.3-17.el7cp

How reproducible:
Always

- If we upgrade hammer to jewel and metadata gets converted successfully from hammer to jewel, we log a message:

~~~
2017-02-11 00:09:56.704029 7f9011d259c0  0 System already converted 
~~~

- Now because this log message is at log level 0, it is getting printed in each and every simple 'radosgw-admin' command:

~~~
# radosgw-admin user info --uid testuser
2017-02-11 00:09:56.704029 7f9011d259c0  0 System already converted 
{
    "user_id": "testuser",
    "display_name": "Test User1",
    "email": "",
~~~