Add cobbler inventory plugin (#627)

* Add cobbler inventory plugin

* Add elements, caps

* Use fail_json if we cannot import xmlrpc_client

* [cobbler] Raise AnsibleError for errors

* [plugins/inventory/cobbler] Add cache_fallback option

* [inventory/cobbler] Use != for comparison

* [inventory/cobbler] Add very basic unit tests

* Update plugins/inventory/cobbler.py

Use full name

Co-authored-by: Felix Fontein <felix@fontein.de>

Co-authored-by: Felix Fontein <felix@fontein.de>

tests/unit/plugins/inventory/test_cobbler.py

@@ -0,0 +1,41 @@
+# -*- coding: utf-8 -*-
+
+# Copyright 2020 Orion Poplawski <orion@nwra.com>
+#
+# This file is part of Ansible
+#
+# Ansible is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+import pytest
+import sys
+
+from ansible.errors import AnsibleError, AnsibleParserError
+from ansible_collections.community.general.plugins.inventory.cobbler import InventoryModule
+
+
+@pytest.fixture(scope="module")
+def inventory():
+    return InventoryModule()
+
+
+def test_init_cache(inventory):
+    inventory._init_cache()
+    assert inventory._cache[inventory.cache_key] == {}
+
+
+def test_verify_file_bad_config(inventory):
+    assert inventory.verify_file('foobar.cobber.yml') is False