[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: I381999e669bfe7a603c9233f9c22b6e80abc708b

cinder/coordination.py

@@ -38,6 +38,7 @@ LOG = log.getLogger(__name__)
 
 coordination_opts = [
     cfg.StrOpt('backend_url',
+               secret=True,
                default='file://$state_path',
                help='The backend URL to use for distributed coordination.'),
 ]

releasenotes/notes/bug-2012246-292d7d93260a1fe5.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    `Bug #2008017 <https://bugs.launchpad.net/cinder/+bug/2012246>`_: Hide
+    value of the `[coordination] backend_url` option from logs because it can
+    contain credential.