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: I7d8b22d8a6220f176cb8812f9ae37f64998d56dc

.zuul.yaml

@@ -3,7 +3,6 @@
       - check-requirements
       - openstack-lower-constraints-jobs
       - openstack-python-jobs
-      - openstack-python35-jobs
       - openstack-python36-jobs
       - openstack-python37-jobs
       - publish-openstack-docs-pti

setup.cfg

@@ -8,7 +8,6 @@ classifiers =
     Programming Language :: Python :: 2
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.5
     Programming Language :: Python :: 3.6
     Environment :: OpenStack
     Intended Audience :: Information Technology

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py37,py36,py35,py27,pep8
+envlist = py37,py36,py27,pep8
 minversion = 2.0
 skipsdist = True
 
@@ -20,8 +20,8 @@ passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
 basepython = python2.7
 commands = oslo_debug_helper -t sahara_plugin_vanilla/tests/unit {posargs}
 
-[testenv:debug-py35]
-basepython = python3.5
+[testenv:debug-py36]
+basepython = python3.6
 commands = oslo_debug_helper -t sahara_plugin_vanilla/tests/unit {posargs}
 
 [testenv:pep8]