Make all doc fragments, module utils, and plugin utils private (#11896)

* Make all doc fragments private.

* Make all plugin utils private.

* Make all module utils private.

* Reformat.

* Changelog fragment.

* Update configs and ignores.

* Adjust unit test names.

tests/unit/plugins/module_utils/_xenserver/common.py

@@ -0,0 +1,24 @@
+#
+# Copyright (c) 2019, Bojan Vitnik <bvitnik@mainstream.rs>
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+from __future__ import annotations
+
+
+def fake_xenapi_ref(xenapi_class):
+    return f"OpaqueRef:fake-xenapi-{xenapi_class}-ref"
+
+
+testcase_bad_xenapi_refs = {
+    "params": [
+        None,
+        "",
+        "OpaqueRef:NULL",
+    ],
+    "ids": [
+        "none",
+        "empty",
+        "ref-null",
+    ],
+}