Add support for network adapter hotplug.
Add support for network adapter hotplug.

    This patch makes it possible to add/del instance
    interface other than booting time.
    Implement bp:network-adapter-hotplug

Originally from change Ibee003a9ec6cc9b3fd275417caccd0c67f6c871f

Co-authored-by: Yaguang Tang <heut2008@gmail.com>
Co-authored-by: Édouard Thuleau <edouard.thuleau@orange.com>

Change-Id: I4f8f677af58afcb928379e5cf859388d1da45d51

citrix-openstack-build/oslo.versionedobjects,openstack/oslo.versionedobjects