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.

Related-prod: PROD-22634

Change-Id: Ice6474aa7df74948e792b83ec497a5efb8df6764
(cherry picked from commit c7f9b21b96cebfd4fdc29e8b4fad2084f0042556)
(cherry picked from commit 7bbc10e1f413718f44c7767baa0bc96a8169ec93)
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]