use plugin names from neutron-lib plugin constants

Switch usage of plugin names from neutron_lib.constants over to
neutron_lib.plugins.constants in prep for
https://review.openstack.org/#/c/531857/

Change-Id: I86e0cdff4802874644262a7aaa699792f4080451

neutron_vpnaas/db/vpn/vpn_validator.py

@@ -18,8 +18,8 @@ import netaddr
 from neutron.db import l3_db
 from neutron.db import models_v2
 from neutron_lib.api import validators
-from neutron_lib import constants as const
 from neutron_lib import exceptions as nexception
+from neutron_lib.plugins import constants as plugin_const
 from neutron_lib.plugins import directory
 
 from neutron_vpnaas._i18n import _
@@ -42,7 +42,7 @@ class VpnReferenceValidator(object):
         try:
             return self._l3_plugin
         except AttributeError:
-            self._l3_plugin = directory.get_plugin(const.L3)
+            self._l3_plugin = directory.get_plugin(plugin_const.L3)
             return self._l3_plugin
 
     @property

neutron_vpnaas/services/vpn/service_drivers/__init__.py

@@ -16,7 +16,7 @@
 import abc
 
 from neutron.common import rpc as n_rpc
-from neutron_lib import constants
+from neutron_lib.plugins import constants
 from neutron_lib.plugins import directory
 from oslo_log import log as logging
 import oslo_messaging

neutron_vpnaas/tests/unit/services/vpn/service_drivers/test_cisco_ipsec.py

@@ -17,7 +17,6 @@ from six import moves
 
 from neutron.db import servicetype_db as st_db
 from neutron.tests.unit import testlib_api
-from neutron_lib import constants as lib_const
 from neutron_lib import context as n_ctx
 from neutron_lib.plugins import constants
 from neutron_lib.plugins import directory
@@ -398,7 +397,7 @@ class TestCiscoIPsecDriver(testlib_api.SqlTestCase):
         }
 
         l3_plugin = mock.Mock()
-        directory.add_plugin(lib_const.L3, l3_plugin)
+        directory.add_plugin(constants.L3, l3_plugin)
 
         l3_plugin.get_host_for_router.return_value = FAKE_HOST
         l3_agent = mock.Mock()