Fix type mismatch between option and its default

... to avoid the following warning.

```
UserWarning: converting '1' to a string
  warnings.warn('converting \'%s\' to a string' % str_val)
```

Change-Id: I852d63523d3582f00d4d7953199181e3d2b6a885
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

watcher/conf/ironic_client.py

@@ -23,7 +23,7 @@ ironic_client = cfg.OptGroup(name='ironic_client',
 
 IRONIC_CLIENT_OPTS = [
     cfg.StrOpt('api_version',
-               default=1,
+               default='1',
                help='Version of Ironic API to use in ironicclient.'),
     cfg.StrOpt('endpoint_type',
                default='publicURL',