Do not rise exception if OVS Queue is not present when being deleted

In this case, there is no need to raise an exception because the
Queue is not present anymore in the OVS database. A warning message
will be logged.

Change-Id: I836e762bf0703d53f47877b73354948cba70e9c2
Closes-Bug: #1819477

neutron/agent/common/ovs_lib.py

@@ -26,6 +26,7 @@ from neutron_lib.services.qos import constants as qos_constants
 from oslo_config import cfg
 from oslo_log import log as logging
 from oslo_utils import uuidutils
+from ovsdbapp.backend.ovs_idl import idlutils
 import six
 import tenacity
 
@@ -1005,8 +1006,7 @@ class OVSBridge(BaseOVS):
                 self._set_port_qos(port['name'])
             self.ovsdb.db_destroy('QoS', qos_id).execute(check_error=True)
             for queue_uuid in queues.values():
-                self.ovsdb.db_destroy('Queue', queue_uuid).execute(
-                    check_error=True)
+                self._delete_queue(queue_uuid)
 
     def _update_queue(self, port_id, queue_num, max_kbps=None,
                       max_burst_kbps=None, min_kbps=None):
@@ -1059,7 +1059,10 @@ class OVSBridge(BaseOVS):
         return queues
 
     def _delete_queue(self, queue_id):
-        self.ovsdb.db_destroy('Queue', queue_id).execute(check_error=True)
+        try:
+            self.ovsdb.db_destroy('Queue', queue_id).execute(check_error=True)
+        except idlutils.RowNotFound:
+            LOG.info('OVS Queue %s was already deleted', queue_id)
 
     def _update_qos(self, qos_id=None, queues=None):
         queues = queues or {}