Dropping the py35 testing

All the integration testing has been moved to
Bionic now[1] and py3.5 is not tested runtime for
Train or stable/stein[2].

As per below ML thread, we are good to drop the py35
testing now:
http://lists.openstack.org/pipermail/openstack-discuss/2019-April/005097.html

[1] http://lists.openstack.org/pipermail/openstack-discuss/2019-April/004647.html
[2]
https://governance.openstack.org/tc/reference/runtimes/stein.html
https://governance.openstack.org/tc/reference/runtimes/train.html

Change-Id: I0fb9547a3156199a6d2ca66258f7c6afab6d0753

.zuul.yaml

@@ -6,7 +6,6 @@
       - openstack-lower-constraints-jobs
       - openstack-cover-jobs
       - openstack-python-jobs
-      - openstack-python35-jobs
       - openstack-python36-jobs
       - openstack-python37-jobs
       - periodic-stable-jobs

setup.cfg

@@ -18,7 +18,7 @@ classifier =
     Programming Language :: Python :: 2
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.5
+    Programming Language :: Python :: 3.6
     Topic :: Software Development :: Libraries
     Topic :: System :: Distributed Computing
 

tox.ini

@@ -5,7 +5,7 @@ envlist =
   docs,
   pep8,
   py27,
-  py35,
+  py36,
   py37,
   pylint,
   update-states