New hostgroup management module

There is a new hostgroup management module placed in the plugins folder:

  plugins/modules/ipahostgroup.py

The hostgroup module allows to add, remove and disable hosts.

The hostgroup module is as compatible as possible to the Ansible upstream
ipa_hostgroup module, but addtionally offers to ensure member presence and
absence.

Here is the documentation for the module:

  README-hostgroup.md

New example playbooks have been added:

  playbooks/hostgroup/ensure-hostgroup-is-absent.yml
  playbooks/hostgroup/ensure-hostgroup-is-present.yml
  playbooks/hostgroup/ensure-hosts-and-hostgroups-are-absent-in-hostgroup.yml
  playbooks/hostgroup/ensure-hosts-and-hostgroups-are-present-in-hostgroup.yml