remove whitebox configuration in tempest.conf

sync up with removing whitebox tests in tempest

This commit depends on https://review.openstack.org/#/c/46116/

Change-Id: I410583187284c2951d872f6e9465f741decc60bd
Merge "remove whitebox configuration in tempest.conf"
Merge branch 'master' of github.com:openstack-dev/devstack