Drop python 2.7 support and testing

Change-Id: I3ff7a714d5fd61edd72e00c7a454c81724844f99
Closes-bug: #1853372
diff --git a/tox.ini b/tox.ini
index 5ea346d..4c2edbc 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,9 +1,13 @@
 [tox]
-minversion = 2.0
+minversion = 3.1.0
 envlist = pep8
 skipsdist = True
+# this allows tox to infer the base python from the environment name
+# and override any basepython configured in this file
+ignore_basepython_conflict=true
 
 [testenv]
+basepython = python3
 usedevelop = True
 install_command = pip install {opts} {packages}
 setenv =
@@ -14,11 +18,9 @@
 commands = python setup.py test --slowest --testr-args='{posargs}'
 
 [testenv:pep8]
-basepython = python3
 commands = flake8 {posargs}
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [flake8]