New module: xenserver_guest_facts - returns facts of XenServer VMs (#49426)

* Initial commit for xenserver_guest_facts module
* New module: xenserver_guest_facts. Returns facts of XenServer VMs. Module is fully documented.
* Added unit tests for the module
* Moved FakeXenAPI import to a dedicated fixture, other fixes
* Removed unused imports, minor fixes to unit test code

test/units/modules/cloud/xenserver/conftest.py

@@ -0,0 +1,44 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright: (c) 2019, Bojan Vitnik <bvitnik@mainstream.rs>
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+
+from __future__ import absolute_import, division, print_function
+__metaclass__ = type
+
+
+import sys
+import importlib
+import pytest
+
+
+@pytest.fixture(autouse=True)
+def XenAPI():
+    """Imports and returns fake XenAPI module."""
+
+    # Import of fake XenAPI module is wrapped by fixture so that it does not
+    # affect other unit tests which could potentialy also use XenAPI module.
+
+    # First we use importlib.import_module() to import the module and assign
+    # it to a local symbol.
+    fake_xenapi = importlib.import_module('units.module_utils.xenserver.FakeXenAPI')
+
+    # Now we populate Python module cache with imported fake module using the
+    # original module name (XenAPI). That way, any 'import XenAPI' statement
+    # will just load already imported fake module from the cache.
+    sys.modules['XenAPI'] = fake_xenapi
+
+    return fake_xenapi
+
+
+@pytest.fixture
+def xenserver_guest_facts(XenAPI):
+    """Imports and returns xenserver_guest_facts module."""
+
+    # Since we are wrapping fake XenAPI module inside a fixture, all modules
+    # that depend on it have to be imported inside a test function. To make
+    # this easier to handle and remove some code repetition, we wrap the import
+    # of xenserver_guest_facts module with a fixture.
+    from ansible.modules.cloud.xenserver import xenserver_guest_facts
+
+    return xenserver_guest_facts