Avoid pollution and false positives with tox.ini

- removing sitepackages in tox.ini to avoid test env pollution
- skip_missing_interpreters in tox.ini set to False to avoid false
positives by skipping missing interpreters.

Change-Id: I5e76a220a981a83938b06a48fec74533d5702f8b

.zuul.yaml

@@ -0,0 +1,5 @@
+- project:
+    templates:
+      - python35-charm-jobs
+      - openstack-python3-train-jobs
+

tox.ini

@@ -1,13 +1,16 @@
 [tox]
 envlist = pep8,py27,py34,py35
 skipsdist = True
-skip_missing_interpreters = True
+# NOTE(beisner): Avoid build/test env pollution by not enabling sitepackages.
+sitepackages = False
+# NOTE(beisner): Avoid false positives by not skipping missing interpreters.
+skip_missing_interpreters = False
 
 [testenv]
 setenv = VIRTUAL_ENV={envdir}
          PYTHONHASHSEED=0
 install_command =
-  pip install --allow-unverified python-apt {opts} {packages}
+  pip install {opts} {packages}
 commands = ostestr {posargs}
 
 [testenv:py27]
@@ -28,12 +31,25 @@ deps = -r{toxinidir}/test-requirements.txt
 # TODO: Need to write unit tests then remove the following command.
 commands = /bin/true
 
+[testenv:py36]
+basepython = python3.6
+deps = -r{toxinidir}/test-requirements.txt
+# TODO: Need to write unit tests then remove the following command.
+commands = /bin/true
+
+[testenv:py37]
+basepython = python3.7
+deps = -r{toxinidir}/test-requirements.txt
+# TODO: Need to write unit tests then remove the following command.
+commands = /bin/true
+
 [testenv:pep8]
-basepython = python2.7
+basepython = python3
 deps = -r{toxinidir}/test-requirements.txt
 commands = flake8 {posargs}
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [flake8]