Disable pyXY tests on internal CI

this repo has no actual unit tests and when executing test runner
attempts to run actual tempest tests.

The CI job checks the list of default envs before runnning given
tox env. While this is actually wrong (those pyXY envs are
actually auto-generated by tox), removing them from default env
list unblocks our internal CI.

Change-Id: Ice6474aa7df74948e792b83ec497a5efb8df6764
diff --git a/tox.ini b/tox.ini
index d92b3a6..65f4a68 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 minversion = 2.0
-envlist = py35,py27,pypy,pep8
+envlist = pep8
 skipsdist = True
 
 [testenv]