Add tox configuration for lint and testing

.gitignore

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+.tox

test-requirements.txt

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+flake8>=2.2.4,<=2.4.1
+os-testr>=0.4.1
+charm-tools

tox.ini

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+[tox]
+envlist = lint,py27
+skipsdist = True
+
+[testenv]
+setenv = VIRTUAL_ENV={envdir}
+         PYTHONHASHSEED=0
+install_command =
+  pip install --allow-unverified python-apt {opts} {packages}
+commands = ostestr {posargs}
+
+[testenv:py27]
+basepython = python2.7
+deps = -r{toxinidir}/test-requirements.txt
+
+[testenv:lint]
+basepython = python2.7
+deps = -r{toxinidir}/test-requirements.txt
+commands = flake8 {posargs} lib
+
+[testenv:venv]
+commands = {posargs}
+
+[flake8]
+ignore = E402,E226