Add callback function to manage missing hooks

Before https://review.openstack.org/#/c/337043/,
stevedore.NamedExtensionManager returned KeyError
when calling with non-existing names and name_order=True.

After the mentioned change this is not longer true,
so we used the just added on_missing_entrypoints_callback option
to customize the behavior in this cases and make it raise
a custom exception MissingHookError.

Change-Id: I1f1edc0b7a82a16bf9be4113db61ee1cd0080db4
Closes-Bug: #1600141

ironic_inspector/main.py

@@ -411,8 +411,9 @@ class Service(object):
             hooks = [ext.name for ext in
                      plugins_base.processing_hooks_manager()]
         except KeyError as exc:
-            # stevedore raises KeyError on missing hook
-            LOG.critical(_LC('Hook %s failed to load or was not found'),
+            # callback function raises MissingHookError derived from KeyError
+            # on missing hook
+            LOG.critical(_LC('Hook(s) %s failed to load or was not found'),
                          str(exc))
             sys.exit(1)
 

ironic_inspector/plugins/base.py

@@ -149,6 +149,12 @@ _CONDITIONS_MGR = None
 _ACTIONS_MGR = None
 
 
+def missing_entrypoints_callback(names):
+    """Raise MissingHookError with comma-separated list of missing hooks"""
+    missing_names = ', '.join(names)
+    raise MissingHookError(missing_names)
+
+
 def processing_hooks_manager(*args):
     """Create a Stevedore extension manager for processing hooks.
 
@@ -164,6 +170,7 @@ def processing_hooks_manager(*args):
             names=names,
             invoke_on_load=True,
             invoke_args=args,
+            on_missing_entrypoints_callback=missing_entrypoints_callback,
             name_order=True)
     return _HOOKS_MGR
 
@@ -204,3 +211,7 @@ def rule_actions_manager():
                                 'actions is deprecated (action "%s")'),
                             act.name)
     return _ACTIONS_MGR
+
+
+class MissingHookError(KeyError):
+    """Exception when hook is not found when processing it."""

ironic_inspector/test/unit/test_main.py

@@ -626,7 +626,6 @@ class TestInit(test_base.BaseTest):
         self.service.init()
         self.assertFalse(mock_firewall.called)
 
-    @unittest.skip('skipped until stevedore > 1.15.0 is released')
     @mock.patch.object(main.LOG, 'critical')
     def test_init_failed_processing_hook(self, mock_log, mock_node_cache,
                                          mock_get_client, mock_auth,