Revert "Add back loading of the discovery image, was accidentally removed previously"
Revert "Add back loading of the discovery image, was accidentally removed previously"

This was supposed to be removed since discovery images are not consumable via
glance.

This reverts commit 11c22c9d9e83459cdb92d833ed6c781360b1808e.

dpkshetty/instack-undercloud,eprasad/instack-undercloud,eprasad/instack-undercloud,agroup/instack-undercloud,rdo-management/instack-undercloud,bcrochet/instack-undercloud,dpkshetty/instack-undercloud,rdo-management/instack-undercloud,dmsimard/instack-undercloud,agroup/instack-undercloud,dmsimard/instack-undercloud,bcrochet/instack-undercloud