skip unnecessary steps during tox tests

Author: jesterhazy

tox.ini

@@ -60,21 +60,27 @@ commands =
 deps = .[test]
 
 [testenv:flake8]
-basepython = python
+basepython = python3
+skipdist = true
+skip_install = true
 deps =
     flake8
     flake8-future-import
 commands = flake8
 
 [testenv:pylint]
 basepython = python3
+skipdist = true
+skip_install = true
 deps =
     pylint==2.3.1
 commands =
     python -m pylint --rcfile=.pylintrc -j 0 src/sagemaker
 
 [testenv:twine]
-basepython = python
+basepython = python3
+skipdist = true
+skip_install = true
 # twine check was added starting in 1.12.0
 # https://github.com/pypa/twine/blob/master/docs/changelog.rst
 deps =
@@ -86,6 +92,8 @@ commands =
 
 [testenv:sphinx]
 basepython = python3
+skipdist = true
+skip_install = true
 changedir = doc
 # Based on: https://github.com/rtfd/readthedocs.org/blob/8f0c78dde5edcc85acf90462a8518735a25482d3/readthedocs/doc_builder/python_environments.py#L263
 install_command = python -m pip install --upgrade -I {packages}