sync plugin common constants
sync plugin common constants

Commit Iace31506502de25da9dce5fcfdbfe2c726bea27f added a new common
plugin constant. This patch syncs it into lib.

Change-Id: I208c976c3e7e43e27e1907ed196af8efccd73f22

openstack/neutron-lib,openstack/neutron-lib,openstack/neutron-lib,openstack/neutron-lib