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: I83701f70249d9151b1e88c96713411f0366e46b3
(cherry picked from commit 188d4446dcf4eb80a27f682c2379ceb3735b21a7)
diff --git a/tox.ini b/tox.ini
index 7b8aeec..798be25 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py27,py35,pep8
+envlist = pep8
 minversion = 0.1
 skipsdist = True