New privilege management module

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

    plugins/modules/ipaprivilege.py

The privilege module allows to ensure presence or absence of privilege
and manage privilege permission memebers.

Here is the documentation for the module:

    README-privilege.md

New example playbooks have been added:

    playbooks/privilege/privilege-absent.yml
    playbooks/privilege/privilege-member-absent.yml
    playbooks/privilege/privilege-member-present.yml
    playbooks/privilege/privilege-present.yml

New tests for the module:

    tests/privilege/test_privilege.yml