Update templates root dir to robottelo tmp dir

[JacobCallahan]

Instead of using a hard-coded value for FOREMAN_TEMPLATE_ROOT_DIR, align it to settings.robottelo.tmp_dir

This should resolve some test failures we're seeing in new CI.

https://github.com/SatelliteQE/robottelo/blob/master/robottelo/constants/init.py#L1756