Fix external_network_id
Fix external_network_id

Make external_network be external_network_id to match the rest of the system.

Change-Id: I9bdeabf5efcead9a5b51779b89cc6dd9552defad

openstack/magnum,Tennyson53/magnum,mjbrewer/testindex,ramielrowe/magnum,sajuptpm/magnum,hongbin/magnum,ArchiFleKs/magnum,hongbin/magnum,ArchiFleKs/magnum,ddepaoli3/magnum,ddepaoli3/magnum,Alzon/SUR,jay-lau/magnum,eshijia/magnum,Tennyson53/SUR,openstack/magnum,sajuptpm/magnum,eshijia/SUR,ChengTiesheng/magnum,eshijia/magnum,LaynePeng/magnum,LaynePeng/magnum,dimtruck/magnum,annegentle/magnum,paulczar/magnum,mjbrewer/testindex,paulczar/magnum,Alzon/SUR,ffantast/magnum,eshijia/SUR,ffantast/magnum,ChengTiesheng/magnum,dimtruck/magnum,ramielrowe/magnum,Tennyson53/SUR,mjbrewer/testindex,Tennyson53/magnum,annegentle/magnum