Enable testing for Python 3.8

Python 3.8 is almost there, so I believe that
it would be nice to have tests for it on CI.

Python 3.8 schedule:
https://www.python.org/dev/peps/pep-0569/#schedule

Author: Jamim

.travis.yml

@@ -28,6 +28,10 @@ matrix:
        env: TOXENV=py37
      - python: 3.7
        env: TOXENV=py37-functional
+     - python: 3.8-dev
+       env: TOXENV=py38
+     - python: 3.8-dev
+       env: TOXENV=py38-functional
 
 install:
   - pip install tox

tox.ini

@@ -1,5 +1,7 @@
 [tox]
-envlist = py27, py35, py36, py37
+envlist =
+   py27, py3{5,6,7,8}
+   py27-functional, py3{5,6,7,8}-functional
 
 [testenv]
 passenv = TOXENV CI TRAVIS TRAVIS_*
@@ -9,7 +11,8 @@ deps = -r{toxinidir}/test-requirements.txt
        -r{toxinidir}/requirements.txt
 commands =
    python -V
-   py.test -vvv -s --ignore=kubernetes/e2e_test
+   !functional: py.test -vvv -s --ignore=kubernetes/e2e_test
+   functional: {toxinidir}/scripts/kube-init.sh py.test -vvv -s []
 
 [testenv:docs]
 commands =
@@ -19,26 +22,6 @@ commands =
 commands =
    {toxinidir}/scripts/update-pycodestyle.sh
 
-[testenv:py27-functional]
-commands =
-   python -V
-   {toxinidir}/scripts/kube-init.sh py.test -vvv -s []
-
-[testenv:py35-functional]
-commands =
-   python -V
-   {toxinidir}/scripts/kube-init.sh py.test -vvv -s []
-
-[testenv:py36-functional]
-commands =
-   python -V
-   {toxinidir}/scripts/kube-init.sh py.test -vvv -s []
-
-[testenv:py37-functional]
-commands =
-   python -V
-   {toxinidir}/scripts/kube-init.sh py.test -vvv -s []
-
 [testenv:coverage]
 commands =
    python -V