Remove keystone catalog backend
Remove keystone catalog backend

KEYSTONE_CATALOG_BACKEND is deprecated and removed post Newton [1].
This needs to be removed in Tacker as well to avoid gate failure.

[1] https://review.openstack.org/#/c/278333

Co-Authored-By: Tung Doan <doantungbk.203@gmail.com>

Change-Id: I021e4a4ef0240f85e6cce7feda431d6695f4482b

openstack/tacker,openstack/tacker,openstack/tacker,zeinsteinz/tacker,stackforge/tacker,zeinsteinz/tacker,stackforge/tacker