Avoid pollution and false positives with tox.ini

- updated testenv:build to aim to a tmp build directory
- added missing env
- 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: I8d5af206e2af881013b1f78f7cc913036e6b23c2

tox.ini

@@ -2,6 +2,10 @@
 skipsdist = True
 envlist = pep8
 toxworkdir = /tmp/tox
+# 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]
 basepython = python3
@@ -17,15 +21,52 @@ deps =
 whitelist_externals = /bin/true /bin/echo /bin/mkdir
 
 [testenv:build]
+# ``charm build`` refuses to output to a subdirectory to the source tree
+# The gate check will look for and validate the built artifacts in the source
+# tree.
+# Build the artifats under /tmp and link back to source directory to alleviate.
+basepython = python3
 commands =
   /bin/echo 'WARNING: *build* target is for testing only.'
   /bin/mkdir -p {envdir}/tmp
   charm-build --log-level DEBUG -o {envdir}/tmp/build .
+  /bin/ln -s {envdir}/tmp/build/builds {envdir}/tmp/build/trusty
+  /bin/ln -s {envdir}/tmp/build {toxinidir}/build
 
 [testenv:venv]
 basepython = python3
 commands = {posargs}
 
+[testenv:py27]
+basepython = python2.7
+deps = -r{toxinidir}/test-requirements.txt
+# TODO: Need to write unit tests then remove the following command.
+commands = /bin/true
+
+[testenv:py34]
+basepython = python3.4
+deps = -r{toxinidir}/test-requirements.txt
+# TODO: Need to write unit tests then remove the following command.
+commands = /bin/true
+
+[testenv:py35]
+basepython = python3.5
+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 = python3
 commands = flake8 --ignore=E402 actions/ reactive/