New Role management module

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

    plugins/modules/iparole.py

The role module allows to ensure presence or absence of roles and
manage role members.

Here is the documentation for the module:

    README-role.md

New example playbooks have been added:

    playbooks/role/role-is-absent.yml
    playbooks/role/role-is-present.yml
    playbooks/role/role-member-group-absent.yml
    playbooks/role/role-member-group-present.yml
    playbooks/role/role-member-host-absent.yml
    playbooks/role/role-member-host-present.yml
    playbooks/role/role-member-hostgroup-absent.yml
    playbooks/role/role-member-hostgroup-present.yml
    playbooks/role/role-member-privilege-absent.yml
    playbooks/role/role-member-privilege-present.yml
    playbooks/role/role-member-service-absent.yml
    playbooks/role/role-member-service-present.yml
    playbooks/role/role-member-user-absent.yml
    playbooks/role/role-member-user-present.yml
    playbooks/role/role-members-absent.yml
    playbooks/role/role-members-present.yml
    playbooks/role/role-rename.yml

New tests for the module:

    tests/role/test_role.yml
    tests/role/test_role_service_member.yml