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: Ib82c7d4f23a39cd8c65f72bbbfafd31141648e63
(cherry picked from commit ad24aa8ba8d29439299621d4fd1d1af00e4cd702)
diff --git a/tox.ini b/tox.ini
index 1f1ce01..ac299fa 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]