Add isort and flake8 to CI (#869)

* Run isort.

* Clean up unused assignments.

* Add flake8 linting step.

tests/unit/plugins/module_utils/openssh/test_cryptography.py

@@ -5,9 +5,9 @@
 # SPDX-License-Identifier: GPL-3.0-or-later
 
 from __future__ import absolute_import, division, print_function
-__metaclass__ = type
 
-import pytest
+
+__metaclass__ = type
 
 import os.path
 from getpass import getuser
@@ -15,17 +15,19 @@ from os import remove, rmdir
 from socket import gethostname
 from tempfile import mkdtemp
 
+import pytest
 from ansible_collections.community.crypto.plugins.module_utils.openssh.cryptography import (
     HAS_OPENSSH_SUPPORT,
     InvalidCommentError,
-    InvalidPrivateKeyFileError,
-    InvalidPublicKeyFileError,
     InvalidKeySizeError,
     InvalidKeyTypeError,
     InvalidPassphraseError,
-    OpensshKeypair
+    InvalidPrivateKeyFileError,
+    InvalidPublicKeyFileError,
+    OpensshKeypair,
 )
 
+
 DEFAULT_KEY_PARAMS = [
     (
         'rsa',