[coordination] backend_url should be secret

The backend_url option can sometimes contain secrets.

For example when redis coordination backend is used and authentication
is enabled in redis, the plain redis password is put as an URL element.

[coordination]
backend_url=redis://:password@127.0.0.1:6379

Closes-Bug: #2012246
Change-Id: If0f142a742d407e5e91e422ef3109002b37c475d

ironic_inspector/conf/coordination.py

@@ -22,6 +22,7 @@ from ironic_inspector.common.i18n import _
 _OPTS = [
     cfg.StrOpt('backend_url',
                default='memcached://localhost:11211',
+               secret=True,
                help=_('The backend URL to use for distributed coordination. '
                       'EXPERIMENTAL.')),
 ]