[magnum] Fix dib elements path
The diskimage-builder elements location has changed [1].
[1]
source ./env/bin/activate
set -u
- DIB_ELEMENTS=./openstack/diskimage-builder/elements
+ DIB_ELEMENTS=./openstack/diskimage-builder/diskimage_builder/elements
if [ "{image-name}" == "ubuntu-mesos" ]; then
TRIPLEO_ELEMENTS=./openstack/tripleo-image-elements/elements
