mgr/cephadm: fixup expected extra ceph conf test result

mgr/cephadm: fixup expected extra ceph conf test result

fix test failure introduced by:
ff7e76348e5457fa6acb23545fcef56d6640c50a

```
E           AssertionError: expected call not found.
E           Expected: _run_cephadm('test', 'mon.test', 'deploy', ['--name', 'mon.test', '--reconfig', '--config-json', '-'], stdin='{"config": "\\n\\n[mon]\\nk=v\\n", "keyring": ""}')
E           Actual: _run_cephadm('test', 'mon.test', 'deploy',
['--name', 'mon.test', '--reconfig', '--config-json', '-'],
stdin='{"config": "\\n\\n[mon]\\nk=v\\n", "keyring": ""}', image='')
```

Signed-off-by: Michael Fritch <mfritch@suse.com>