New idp management module

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

    plugins/modules/ipaidp.py

The idp module allows to ensure presence or absence of external Identity
Providers.

Here is the documentation for the module:

    README-idp.md

New idp example playbooks:

    playbooks/idp/idp-present.yml
    playbooks/idp/idp-absent.yml

New tests for the module:

    tests/idp/test_idp.yml
    tests/idp/test_idp_client_context.yml