Connect nb db in l3 plugin after neutron server fork
Connect nb db in l3 plugin after neutron server fork

The service plugin will be initialized at neutron server startup, before
neutron server fork. This patch just get nb_api from core plugin, so that
the nb db will be connected in core plugin, after neutron server fork

Change-Id: Ic8234f177bc23e655131b9815d3c45e3f83d8e90

openstack/dragonflow,openstack/dragonflow,openstack/dragonflow