Prepare un-flatmapping (#5350)

* Add module name into fixtures directory name.

* Rename conftest.py to avoid collisions.

* Match filenames inside directories.

tests/unit/plugins/modules/system/interfaces_file/interfaces_file-README.md

@@ -15,7 +15,7 @@ SPDX-License-Identifier: GPL-3.0-or-later
 
 1. Clone project to `ansible_collections/community/general`
 2. Change directory to the project one `cd ansible_collections/community/general`
-3. Run `ansible-test units --docker -v --python 3.6 tests/unit/plugins/modules/system/interfaces_file/test_interfaces_file.py`
+3. Run `ansible-test units --docker -v --python 3.10 tests/unit/plugins/modules/system/interfaces_file/test_interfaces_file.py`
 
 ## Adding tests
 
@@ -23,5 +23,5 @@ SPDX-License-Identifier: GPL-3.0-or-later
 2. New test cases should be defined in `test_interfaces_file.py`. Same for new test functions if needed
 3. On first test run for a new combination of a test case and an interface configuration new set of golden files will be generated. In case of docker-based test approach that's going to fail due to RO mount option. The workaround is to run tests locally with Python 3 (3.7 in this example):
     1. Install required modules with `pip3.7 install pytest-xdist pytest-mock mock`
-    3. Run tests with `ansible-test units --python 3.7 tests/unit/plugins/modules/system/interfaces_file/test_interfaces_file.py`
+    3. Run tests with `ansible-test units --python 3.10 tests/unit/plugins/modules/system/interfaces_file/test_interfaces_file.py`
 4. Carefully verify newly created golden output files!