Add tox targets for functional testing on 2 and 3

Previously, the functional tests would run using the `python` in your
environment, which was 3 for myself and 2 for most others. We should
really be testing on both versions as we do for unit tests. A change to
the gate will follow this.

Change-Id: I2bd2664018c135593a96fd6ba5741279da772e76
Closes-Bug: 1489935

doc/source/contributors/testing.rst

@@ -82,15 +82,19 @@ Replace ``xxx.xxx.xxx.xxx`` with the IP address or FQDN of your DevStack instanc
 Run
 ***
 
-In order to run the entire functional test suite, simply run the
-``tox -e functional`` command inside of your source checkout. This will
+Functional tests are run against both Python 2 and 3. In order to run the
+entire functional test suite, run the ``tox -e functional`` and
+``tox -e functional3`` command inside of your source checkout. This will
 attempt to run every test command under ``/openstack/tests/functional/``
-in the source tree. The functional tests are run with your system Python
-interpreter. You should run the full functional test suite before submitting
-changes for review in order to avoid unexpected failures in the continuous
-integration system.::
+in the source tree. You should run the full functional test suite before
+submitting changes for review in order to avoid unexpected failures in
+the continuous integration system.::
 
    (sdk3)$ tox -e functional
    ...
    functional: commands succeeded
    congratulations :)
+   (sdk3)$ tox -e functional3
+   ...
+   functional3: commands succeeded
+   congratulations :)

tox.ini

@@ -11,10 +11,20 @@ setenv =
 deps = -r{toxinidir}/test-requirements.txt
 commands = ostestr {posargs}
 
-[testenv:functional]
+[functionalbase]
 setenv = OS_TEST_PATH=./openstack/tests/functional
 passenv = OS_*
 
+[testenv:functional]
+basepython = python2.7
+setenv = {[functionalbase]setenv}
+passenv = {[functionalbase]passenv}
+
+[testenv:functional3]
+basepython = python3.4
+setenv = {[functionalbase]setenv}
+passenv = {[functionalbase]passenv}
+
 [testenv:pep8]
 commands = flake8