Run CI in an environment that includes Python, and test generated code (#2072)

* CI: use a docker image that includes Python

So that tests of abi-gen generating Python can exercise the code being
generated.

* CI fix: disable old yarn permission denied hack

Motivated by CI failure of previous commit.

* CI fix: more resources for test-contracts-ganache

Motivated by CI failure of previous commit.

* CI fix: remove hack of permissions for python libs

Fix for previous CI run's failure of test-python.  Apparently we don't
need this in the docker container we've switched to.

* abi-gen/Py: minimum viable test of gen'd code

Ensure the code is parseable by running it through black.

* abi-gen/Py: expand Python linter usage

Make abi-gen filter its output through black, if its available in the
runtime environment.  Accordingly, stop having contract_wrappers.py's
setup.py pre_install run black on copied-over files.

Adds Pylint to the list of linters run against test-cli/output.

* abi-gen: re-enable Solidity linter

It was broken, running seemingly cleanly but not actually reading any
files, because it was targetting the wrong folder.

* abi-gen/test-cli/fixtures/sol: fix linter errors

* abi-gen/test-cli: disable pylint blackisted-name

* abi-gen/Py: rm unused var in contracts w/o methods

Remove unused variable from generated wrapper for contracts without any
methods.

python-packages/contract_wrappers/setup.py

@@ -7,7 +7,6 @@ from shutil import copy, rmtree
 from os import environ, path, remove
 from pathlib import Path
 from sys import argv
-from importlib.util import find_spec
 
 from distutils.command.clean import clean
 import distutils.command.build_py
@@ -15,9 +14,6 @@ from setuptools import find_packages, setup
 from setuptools.command.test import test as TestCommand
 
 
-BLACK_COMMAND = "black --line-length 79 "
-
-
 CONTRACTS_TO_BE_WRAPPED = [
     "asset_proxy_owner",
     "coordinator",
@@ -82,16 +78,6 @@ class PreInstallCommand(distutils.command.build_py.build_py):
                     pkgdir, "src", "zero_ex", "contract_wrappers", contract
                 ),
             )
-        if find_spec("black") is None:
-            subprocess.check_call("pip install black".split())  # nosec
-        black_command = BLACK_COMMAND + " ".join(
-            [
-                f"src/zero_ex/contract_wrappers/{contract}/__init__.py"
-                for contract in CONTRACTS_TO_BE_WRAPPED
-            ]
-        )
-        print(f"Running command `{black_command}`...")
-        subprocess.check_call(black_command.split())  # nosec
 
 
 class TestCommandExtension(TestCommand):
@@ -114,7 +100,9 @@ class LintCommand(distutils.command.build_py.build_py):
         """Run linter shell commands."""
         lint_commands = [
             # formatter:
-            (BLACK_COMMAND + " --check --diff src test setup.py").split(),
+            (
+                "black --line-length 79 --check --diff src test setup.py"
+            ).split(),
             # style guide checker (formerly pep8):
             "pycodestyle src test setup.py".split(),
             # docstring style checker: