Introducing a new var: {{ openstask_host_module_file }} that contain
the path to the file containing module list.
Centos will use systemd-modules-load.service:
- http://www.unix.com/man-page/centos/8/systemd-modules-load.service/
- http://www.unix.com/man-page/centos/5/modules-load.d/
Change-Id: I9ce294045259752e48c47ed036a9550565f05bc5