[func test] refactor interface attach with qos

To make the existing negative detach test more generic the logic is
changed from increasing the resource request of the port over the
resource inventory to decrease the resource inventory below the port
request. This is needed as the way to increasing the port request will
be different when the extended resource request extension is enabled.

Change-Id: Iec9d3bb4fef7b6b18a13517872f46afcce02520c
blueprint: qos-minimum-guaranteed-packet-rate

Author: Balazs Gibizer

nova/tests/functional/test_servers_resource_request.py

@@ -1017,11 +1017,16 @@ def test_interface_attach_with_resource_request_no_candidates(self):
             networks=[{'port': self.neutron.port_1['id']}])
         self._wait_for_state_change(server, 'ACTIVE')
 
-        # attach an OVS port with too big resource request
+        # decrease the resource inventory so that the OVS port will not fit
+        self._set_provider_inventories(
+            self.ovs_bridge_rp_per_host[self.compute1_rp_uuid],
+            {"inventories": {
+                orc.NET_BW_IGR_KILOBIT_PER_SEC: {"total": 10},
+                orc.NET_BW_EGR_KILOBIT_PER_SEC: {"total": 10},
+            }})
+
+        # try to attach an OVS port with too big resource request
         ovs_port = self.neutron.port_with_resource_request
-        resources = self.neutron._ports[
-            ovs_port['id']]['resource_request']['resources']
-        resources['NET_BW_IGR_KILOBIT_PER_SEC'] = 1000000
 
         post = {
             'interfaceAttachment': {
@@ -1033,6 +1038,9 @@ def test_interface_attach_with_resource_request_no_candidates(self):
 
         self.assertEqual(400, ex.response.status_code)
         self.assertIn('Failed to allocate additional resources', str(ex))
+        self.assertNotIn(
+            'Failed to retrieve allocation candidates from placement API',
+            self.stdlog.logger.output)
 
     def test_interface_attach_with_resource_request_pci_claim_fails(self):
         # boot a server with a single SRIOV port that has no resource request