Update manual guide to not harcode br-ex
Update manual guide to not harcode br-ex

Make it same as quick guide to get public interface

Closes-Bug: #1477793
Change-Id: I69c74c01aa196c6150148798a43d413f0cc7e84f

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