Skip amphora scenario test if provider is not set

This patch also removes py27 and py35 from list of envs in tox. We don't
have functional tests.

Change-Id: Id9255fe87d61bf6536c8d03f9dd7612abc451904
diff --git a/tox.ini b/tox.ini
index d7d9ddd..64afde0 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 minversion = 2.0
-envlist = py35,py27,pep8
+envlist = pep8
 skipsdist = True
 
 [testenv]