atomic: update lorax passed vars
Add new ostree_install_repo and ostree_update_repo vars so that we
can tell lorax where to pull from during the pungi compose and also
where to configure an installed system to pull from. i.e. where a
user is going to pull from over time.
This is related to https://pagure.io/fedora-lorax-templates/pull-request/19
Signed-off-by: Dusty Mabe <dusty@dustymabe.com>