Create tox file and support configuration files

This supports stestr unit tests as well linting with pep8 / flake8

.stestr.conf

+[DEFAULT]
+test_path=./devices/test
+top_dir=./
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test-requirements.txt

+# The order of packages is significant, because pip processes them in the order
+# of appearance. Changing the order has an impact on the overall integration
+# process, which may cause wedges in the gate later.
+
+coverage>=5.2.0 # Apache-2.0
+doc8>=0.8.0 # Apache-2.0
+hacking>=3.2.0,<3.3.0 # Apache-2.0
+#mypy>=0.812 # MIT
+python-subunit>=1.4.0 # Apache-2.0/BSD
+Pygments>=2.6.0
+#oslotest>=4.4.0 # Apache-2.0
+#oslo.messaging>=12.2.0 # Apache-2.0
+stestr>=3.0.0 # Apache-2.0
+testscenarios>=0.5.0 # Apache-2.0/BSD
+testtools>=2.4.0 # MIT
+bandit>=1.6.0 # Apache-2.0
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tox.ini

+[tox]
+minversion = 2.0
+envlist = py36,py37,py38,py39,pep8
+skipsdist = True
+
+[testenv]
+usedevelop = True
+install_command = pip3 install {opts} {packages}
+setenv =
+   VIRTUAL_ENV={envdir}
+   PYTHONWARNINGS=default::DeprecationWarning
+   OS_STDOUT_CAPTURE=1
+   OS_STDERR_CAPTURE=1
+   OS_TEST_TIMEOUT=60
+deps = -r{toxinidir}/test-requirements.txt
+commands = stestr run {posargs}
+
+[testenv:pep8]
+commands =
+;    doc8 doc/source/ README.rst
+    flake8 {posargs}
+    bandit -r devices -x test -n5 -ll # -s B320
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