[VNC OpenStack] Support the neutron lib decomposition

From recent neutron release (since newton), a reusable library code for
neutron names 'neutron-lib' was introduced to stabalize some of the
common interfaces. That patch permits to support that new library.

Change-Id: I0993a8da25bd8c38826c3b0d8f86ff3a0e667586
Closes-Bug: #1650339

src/config/vnc_openstack/vnc_openstack/neutron_plugin_db.py

@@ -17,7 +17,10 @@
 import gevent
 import bottle
 
-from neutron.common import constants
+try:
+    from neutron_lib import constants
+except ImportError:
+    from neutron.common import constants
 
 from cfgm_common import exceptions as vnc_exc
 from vnc_api.vnc_api import *
@@ -129,7 +132,7 @@ class DBInterface(object):
     Q_URL_PREFIX = '/extensions/ct'
 
     def __init__(self, manager, admin_name, admin_password, admin_tenant_name,
-                 api_srvr_ip, api_srvr_port, 
+                 api_srvr_ip, api_srvr_port,
                  api_server_obj=None, user_info=None,
                  contrail_extensions_enabled=True,
                  list_optimization_enabled=False,