OPENSTACK-2959: we need to update port before build service object

when migrate lb tree from A device to B device, agent use network
information from service object.

so when need to update network first, then build network info into
service object.

then the agent can use new network (physical info, vlan) from
service object.

Author: zhang-shengping

f5lbaasdriver/v2/bigip/driver_v2.py

@@ -810,16 +810,17 @@ def refresh(self, context, body):
         try:
             agent, device = self._schedule_agent_and_device(
                 context, loadbalancer, device_id=device_id)
+
+            if device_id:
+                self.migrate_vipport(context, agent, device, loadbalancer)
+
             # NOTE(qzhao): Call agent to rebuild LB.
             service = self._create_service(context, loadbalancer, agent)
 
             device["rm_selfip_port"] = rm_selfip_port
             service["device"] = device
             agent_host = agent['host']
 
-            if device_id:
-                self.migrate_vipport(context, agent, device, loadbalancer)
-
             if rebuild_all:
                 self._allocate_acl_groups(context, service)
                 driver.agent_rpc.rebuild_loadbalancer(