Marking the login_url option as "deprecated_for_removal"
Marking the login_url option as "deprecated_for_removal"

https://review.openstack.org/#/c/212239 has been successfully
merged and now we don't need the login_url option because only
the dashboard_url option is used in the dashboard test. This patch
is intended to mark CONF.dashboard.login_url as deprecated_for_removal.

Change-Id: I4195478d93da605218fddf9aa896e2804ab442ac

vedujoshi/tempest,izadorozhna/tempest,zsoltdudas/lis-tempest,xbezdick/tempest,openstack/tempest,zsoltdudas/lis-tempest,LIS/lis-tempest,flyingfish007/tempest,dkalashnik/tempest,Tesora/tesora-tempest,dkalashnik/tempest,Tesora/tesora-tempest,izadorozhna/tempest,rakeshmi/tempest,vedujoshi/tempest,xbezdick/tempest,cisco-openstack/tempest,flyingfish007/tempest,LIS/lis-tempest,bigswitch/tempest,pczerkas/tempest,cisco-openstack/tempest,tonyli71/tempest,sebrandon1/tempest,masayukig/tempest,tonyli71/tempest,Juniper/tempest,bigswitch/tempest,sebrandon1/tempest,openstack/tempest,Juniper/tempest,rakeshmi/tempest,masayukig/tempest,pczerkas/tempest