Fix BigSwitch plugin to handle device_id re-use in porttracker code

Updates the BigSwitch port_tracker code to use the sqlalchemy merge method
instead of the add method for the port location tracking code to avoid primary
 key constraint errors if device-ids are moved or re-used

Fixes: bug #1208990
Change-Id: I06065ac888873b00f445d4356b17f084ee38c1ea

neutron/plugins/bigswitch/db/porttracker_db.py

@@ -47,4 +47,4 @@ def put_port_hostid(context, port_id, host_id):
         return
     with context.session.begin(subtransactions=True):
         location = PortLocation(port_id=port_id, host_id=host_id)
-        context.session.add(location)
+        context.session.merge(location)

neutron/tests/unit/bigswitch/test_restproxy_plugin.py

@@ -190,6 +190,16 @@ def test_port_vif_details(self):
         with self.port(**kwargs) as port:
             self.assertEqual(port['port']['binding:vif_type'], self.VIF_TYPE)
 
+    def test_port_move(self):
+        kwargs = {'name': 'name', 'binding:host_id': 'ivshost',
+                  'device_id': 'override_dev'}
+        with self.port(**kwargs) as port:
+            data = {'port': {'binding:host_id': 'someotherhost',
+                             'device_id': 'override_dev'}}
+            req = self.new_update_request('ports', data, port['port']['id'])
+            res = self.deserialize(self.fmt, req.get_response(self.api))
+            self.assertEqual(res['port']['binding:vif_type'], self.VIF_TYPE)
+
     def _make_port(self, fmt, net_id, expected_res_status=None, **kwargs):
         res = self._create_port(fmt, net_id, expected_res_status,
                                 ('binding:host_id', ), **kwargs)