New automount key management module

There is a new automount key module placed in the plugins folder:

    plugins/modules/ipaautomountkey.py

The server module allows to ensure presence and absence of automount
keys. The module requires an existing automount location and map to
place the key within.

Here is the documentation for the module:

    README-automountkey.md

New example playbooks have been added:

    playbooks/automount/automount-key-absent.yaml
    playbooks/automount/automount-key-present.yaml

New tests for the module:

    tests/automount/test_automountkey.yml