python: add avocado-framework and tests

Try using avocado to manage our various tests; even though right now
they're only invoking shell scripts and not really running any
python-native code.

Create tests/, and add shell scripts which call out to mypy, flake8,
pylint and isort to enforce the standards in this directory.

Add avocado-framework to the setup.cfg development dependencies, and add
avocado.cfg to store some preferences for how we'd like the test output
to look.

Finally, add avocado-framework to the Pipfile environment and lock the
new dependencies. We are using avocado >= 87.0 here to take advantage of
some features that Cleber has helpfully added to make the test output
here *very* friendly and easy to read for developers that might chance
upon the output in Gitlab CI.

[Note: ALL of the dependencies get updated to the most modern versions
that exist at the time of this writing. No way around it that I have
seen. Not ideal, but so it goes.]

Provided you have the right development dependencies (mypy, flake8,
isort, pylint, and now avocado-framework) You should be able to run
"avocado --config avocado.cfg run tests/" from the python folder to run
all of these linters with the correct arguments.

(A forthcoming commit adds the much easier 'make check'.)

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Tested-by: Cleber Rosa <crosa@redhat.com>
Message-id: 20210527211715.394144-28-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

python/setup.cfg

@@ -25,6 +25,7 @@ packages =
 [options.extras_require]
 # Run `pipenv lock --dev` when changing these requirements.
 devel =
+    avocado-framework >= 87.0
     flake8 >= 3.6.0
     isort >= 5.1.2
     mypy >= 0.770