Make identity interface configurable

Keystone middleware sets the default identity interface as "internal".
This was causing issues with DevStack where "internal" endpoints
weren't being created.

We added a new config for interface, and have it default to 'public'.

Task: 41593
Story: 2008515
Change-Id: Ib8e546d5fbfbcb561e5b139893605d05c1a8ad62

adjutant/config/identity.py

@@ -134,4 +134,12 @@ _auth_group.register_child_config(
         required_for_tests=False,
     )
 )
+_auth_group.register_child_config(
+    fields.StrConfig(
+        "interface",
+        help_text="Keystone endpoint interface type.",
+        default="public",
+        required=True,
+    )
+)
 config_group.register_child_config(_auth_group)

adjutant/wsgi.py

@@ -44,6 +44,7 @@ conf = {
     "project_domain_id": CONF.identity.auth.project_domain_id,
     "user_domain_id": CONF.identity.auth.user_domain_id,
     "auth_url": CONF.identity.auth.auth_url,
+    "interface": CONF.identity.auth.interface,
     "delay_auth_decision": True,
     "include_service_catalog": False,
     "token_cache_time": CONF.identity.token_cache_time,