Log missing clients as WARNING instead of ERROR

This will prevent tracebacks from being logged if every client is not
installed when the engine is started.

Change-Id: I53c90f98689070a0b18e49ca7988e4176a8987ac
Closes-Bug: #1597593

heat/common/pluginutils.py

@@ -0,0 +1,24 @@
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from oslo_log import log as logging
+
+LOG = logging.getLogger(__name__)
+
+
+def log_fail_msg(manager, entrypoint, exception):
+    LOG.warning('Encountered exception while loading %(module_name)s: '
+                '"%(message)s". Not using %(name)s.' %
+                {'module_name': entrypoint.module_name,
+                 'message': exception.message,
+                 'name': entrypoint.name})

heat/engine/clients/__init__.py

@@ -22,6 +22,7 @@ from stevedore import enabled
 from heat.common import exception
 from heat.common.i18n import _
 from heat.common.i18n import _LW
+from heat.common import pluginutils
 
 LOG = logging.getLogger(__name__)
 
@@ -130,7 +131,8 @@ def initialise():
     _mgr = enabled.EnabledExtensionManager(
         namespace='heat.clients',
         check_func=client_is_available,
-        invoke_on_load=False)
+        invoke_on_load=False,
+        on_load_failure_callback=pluginutils.log_fail_msg)
 
 
 def list_opts():

heat/engine/resources/__init__.py

@@ -13,6 +13,7 @@
 
 from stevedore import extension
 
+from heat.common import pluginutils
 from heat.engine import clients
 from heat.engine import environment
 from heat.engine import plugin_manager
@@ -42,7 +43,8 @@ def _register_event_sinks(env, type_pairs):
 def _get_mapping(namespace):
     mgr = extension.ExtensionManager(
         namespace=namespace,
-        invoke_on_load=False)
+        invoke_on_load=False,
+        on_load_failure_callback=pluginutils.log_fail_msg)
     return [[name, mgr[name].plugin] for name in mgr.names()]