Support custom container registry for database images

Currently, trove guest agent is pulling container images from docker
hub, it's impossible to use private container registry, this patch
is adding that support.

Change-Id: I3d14810b43acbf5d2fe6afcc138d476e366042f4

releasenotes/notes/wallaby-docker-registry.yaml

@@ -0,0 +1,4 @@
+---
+features:
+  - Added custom container registry configuration for trove guest agent, it's
+    now possible to use images in private registry rather than docker hub.

trove/common/cfg.py

@@ -1500,6 +1500,24 @@ service_credentials_opts = [
                help="Keystone region name of the Trove service project."),
 ]
 
+guest_agent_group = cfg.OptGroup(
+    'guest_agent', title='Guest Agent options',
+    help="Config options used by guest agent.")
+guest_agent_opts = [
+    cfg.StrOpt(
+        'container_registry',
+        help='URL to the registry. E.g. https://index.docker.io/v1/'
+    ),
+    cfg.StrOpt(
+        'container_registry_username',
+        help='The registry username.'
+    ),
+    cfg.StrOpt(
+        'container_registry_password',
+        help='The plaintext registry password.'
+    ),
+]
+
 CONF = cfg.CONF
 
 CONF.register_opts(path_opts)
@@ -1522,6 +1540,7 @@ CONF.register_group(db2_group)
 CONF.register_group(mariadb_group)
 CONF.register_group(network_group)
 CONF.register_group(service_credentials_group)
+CONF.register_group(guest_agent_group)
 
 CONF.register_opts(mysql_opts, mysql_group)
 CONF.register_opts(percona_opts, percona_group)
@@ -1537,6 +1556,7 @@ CONF.register_opts(db2_opts, db2_group)
 CONF.register_opts(mariadb_opts, mariadb_group)
 CONF.register_opts(network_opts, network_group)
 CONF.register_opts(service_credentials_opts, service_credentials_group)
+CONF.register_opts(guest_agent_opts, guest_agent_group)
 
 CONF.register_opts(rpcapi_cap_opts, upgrade_levels)
 
@@ -1557,6 +1577,7 @@ def list_opts():
         (mariadb_group, mariadb_opts),
         (network_group, network_opts),
         (service_credentials_group, service_credentials_opts),
+        (guest_agent_group, guest_agent_opts),
     ]
 
     return keystone_middleware_opts + keystone_loading_opts + trove_opts

trove/guestagent/datastore/manager.py

@@ -88,6 +88,17 @@ class Manager(periodic_task.PeriodicTasks):
         self.app = None
         self.status = None
 
+        if CONF.guest_agent.container_registry:
+            try:
+                self.docker_client.login(
+                    CONF.guest_agent.container_registry_username,
+                    CONF.guest_agent.container_registry_password,
+                    email="",
+                    registry=CONF.guest_agent.container_registry)
+            except Exception as exc:
+                raise exception.GuestError(f"Failed to login the container "
+                                           f"registry, error: {str(exc)}")
+
     @property
     def manager_name(self):
         """This returns the passed-in name of the manager."""