Allow migrating server with port resource request

Now that the nova code supports such a migration this patch removes the
check from the API that rejected the operation.

Note that in the spec [1] we agreed not to introduce new microversion
for this change but treat it as a bugfix. The current change also makes
it possible to accept the migration of these servers with _any_
microversion.

[1] https://specs.openstack.org/openstack/nova-specs/specs/train/approved/support-move-ops-with-qos-ports.html#rest-api-impact

Change-Id: I4bda569cc7c247e83219276282724c77e760ddcd
blueprint: support-move-ops-with-qos-ports

api-guide/source/port_with_resource_request.rst

@@ -18,9 +18,14 @@ However the following API operations are still not supported in nova:
 * Attaching Neutron ports and networks having QoS minimum bandwidth rule is not
   supported.
 
+Also the following API operations are not supported in the 19.0.0 (Stein)
+version of nova:
+
 * Moving (resizing, migrating, live-migrating, evacuating, unshelving after
   shelve offload) servers with ports having resource request is not yet
   supported.
 
-See :nova-doc:`the admin guide <admin/port_with_resource_request.html>` for
-administrative details.
+As of 20.0.0 (Train), nova supports cold migrating servers with neutron ports
+having resource requests if both the source and destination compute services
+are upgraded to 20.0.0 (Train) and the ``[upgrade_levels]/compute``
+configuration does not prevent the computes from using the latest RPC version.