Set DB retry for quota_enforcement pecan_wsgi hook

The hook starts a DB transaction and should be covered with
DB retry decorator.

Closes-Bug: #1777965
Closes-Bug: #1771293
Change-Id: I044980a98845edc7b0a02e3323a1e62eb54c10c7

neutron/pecan_wsgi/hooks/quota_enforcement.py

@@ -61,6 +61,7 @@ class QuotaEnforcementHook(hooks.PecanHook):
         # retrieved in the 'after' hook
         state.request.context['reservations'] = reservations
 
+    @db_api.retry_db_errors
     def after(self, state):
         neutron_context = state.request.context.get('neutron_context')
         if not neutron_context:

neutron/quota/resource_registry.py

@@ -61,11 +61,6 @@ def set_resources_dirty(context):
     dirty status is True, sets the dirty bit to True in the database
     for the appropriate tenants.
 
-    Please note that this routine begins a nested transaction, and it
-    is not recommended that this transaction begins within another
-    transaction. For this reason the function will raise a SqlAlchemy
-    exception if such an attempt is made.
-
     :param context: a Neutron request context with a DB session
     """
     if not cfg.CONF.QUOTAS.track_quota_usage: