vm: don't delete firewall host in migrate()

circle/vm/models/instance.py

@@ -924,7 +924,7 @@ class Instance(AclBase, VirtualMachineDescModel, TimeStampedModel):
             # Destroy networks
             with act.sub_activity('destroying_net'):
                 for net in self.interface_set.all():
-                    net.destroy()
+                    net.destroy(delete_host=False)
 
             with act.sub_activity('migrate_vm'):
                 queue_name = self.get_remote_queue_name('vm')

circle/vm/models/network.py

@@ -97,11 +97,11 @@ class Interface(Model):
             args=[self.get_vmnetwork_desc()],
             queue=self.instance.get_remote_queue_name('net'))
 
-    def destroy(self, user=None, task_uuid=None):
+    def destroy(self, delete_host=True, user=None, task_uuid=None):
         net_tasks.destroy.apply_async(
             args=[self.get_vmnetwork_desc()],
             queue=self.instance.get_remote_queue_name('net'))
-        if self.host is not None:
+        if delete_host and self.host is not None:
             self.host.delete()
 
     @classmethod