BZ# 1128282 - Remove descendant hostgroups from the foreman host form

Users should not assign hosts directly to the deployment hostgroups.
This removes those choices from the host edit form.
Extend the foreman API to disallow setting the hostgroup via the API
Also remove hostgroups from multiple selected hosts modal
Do not allow the regular hosts controller to accept deployment hg
Merge pull request #330 from bcrochet/bz/1128282

BZ# 1128282 - Remove descendant hostgroups from the foreman host form