[neutron] Get only ID and name of the SGs from Neutron

During the VM booting process Nova asks Neutron for the security groups
of the project. If there are no any fields specified, Neutron will
prepare list of security groups with all fields, including rules.
In case if project got many SGs, it may take long time as rules needs to
be loaded separately for each SG on Neutron's side.

During booting of the VM, Nova really needs only "id" and "name" of the
security groups so this patch limits request to only those 2 fields.

This lazy loading of the SG rules was introduced in Neutron in [1] and
[2].

[1] https://review.opendev.org/#/c/630401/
[2] https://review.opendev.org/#/c/637407/

Related-Bug: #1865223
Change-Id: I15c3119857970c38541f4de270bd561166334548
(cherry picked from commit 388498a)

Author: slawqo

nova/network/neutron.py

@@ -802,9 +802,15 @@ def _process_security_groups(self, instance, neutron, security_groups):
         # TODO(arosen) Should optimize more to do direct query for security
         # group if len(security_groups) == 1
         if len(security_groups):
+            # NOTE(slaweq): fields other than name and id aren't really needed
+            # so asking only about those fields will allow Neutron to not
+            # prepare list of rules for each found security group. That may
+            # speed processing of this request a lot in case when tenant has
+            # got many security groups
+            sg_fields = ['id', 'name']
             search_opts = {'tenant_id': instance.project_id}
             user_security_groups = neutron.list_security_groups(
-                **search_opts).get('security_groups')
+                fields=sg_fields, **search_opts).get('security_groups')
 
             for security_group in security_groups:
                 name_match = None