Set keystone_client default interface to public

Set the default interface for keystone_client to public in the watcher
conf instead of admin.

Closes-Bug: 2109494

Change-Id: I9e0289249981ca965190df6dbdc37e09fd0951d7

releasenotes/notes/bug-2109494-e5bf401767fa6cd6.yaml

@@ -0,0 +1,11 @@
+---
+upgrade:
+  - |
+    The default value of ``[keystone_client] interface`` has been changed from
+    ``admin`` to ``public``.
+fixes:
+  - |
+    When trying to do volume migration using the zone migration strategy, the
+    keystone service is reached, by default through the admin endpoint.
+    The default value of ``[keystone_client] interface`` has been fixed.
+    see Bug https://bugs.launchpad.net/watcher/+bug/2109494 for more info.

watcher/conf/keystone_client.py

@@ -21,7 +21,7 @@ keystone_client = cfg.OptGroup(name='keystone_client',
 
 KEYSTONE_CLIENT_OPTS = [
     cfg.StrOpt('interface',
-               default='admin',
+               default='public',
                choices=['internal', 'public', 'admin'],
                help='Type of endpoint to use in keystoneclient.'),
     cfg.StrOpt('region_name',