New host management module

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

  plugins/modules/ipauser.py

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

The host module is as compatible as possible to the Ansible upstream
ipa_host` module, but addtionally offers to disable hosts.

Here is the documentation for the module:

  README-host.md

New example playbooks have been added:

  playbooks/host/add-host.yml
  playbooks/host/delete-host.yml
  playbooks/host/disable-host.yml