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: If5119930dbdbc3366a330929e2328b96a00c6fe7

.zuul.yaml

@@ -1,7 +1,6 @@
 - project:
     templates:
       - openstack-python-jobs
-      - openstack-python35-jobs
       - openstack-python36-jobs
       - openstack-python37-jobs
       - publish-openstack-docs-pti

setup.cfg

@@ -17,7 +17,7 @@ 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 :: System :: Monitoring
 
 [global]

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 minversion = 1.6
 skipsdist = True
-envlist = py{27,35}{,-mysql,-postgresql},functional,pep8
+envlist = py{27}{,-mysql,-postgresql},functional,pep8
 
 [testenv]
 # NOTE(tonyb): This project has chosen to *NOT* consume upper-constraints.txt