witch python3 versions of test jobs to match Train PTI

In Train, we will use python 3.6 and 3.7 for python3 runtime
in our gate jobs [1]. This commit drops python 3.5 and adds python 3.7.

[1] https://governance.openstack.org/tc/reference/runtimes/train.html

Change-Id: I9628ad9293ea8ccae7d39af564b6713e60d0d4b5

setup.cfg

@@ -16,7 +16,8 @@ classifier =
     Programming Language :: Python :: 2
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.5
+    Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
 
 [files]
 packages =

tox.ini

@@ -1,6 +1,6 @@
 [tox]
-minversion = 2.0
-envlist = py35,py27,pep8,eslint,karma
+minversion = 2.5.0
+envlist = py27,py36,py37,pep8,eslint,karma
 skipsdist = True
 
 [testenv]

zuul.d/projects.yaml

@@ -3,9 +3,7 @@
       - check-requirements
       - horizon-nodejs10-jobs
       - openstack-python-jobs-horizon
-      - openstack-python35-jobs-horizon
-      - openstack-python36-jobs-horizon
-      - openstack-python37-jobs-horizon
+      - openstack-python3-train-jobs-horizon
       - publish-openstack-docs-pti
       - release-notes-jobs-python3
     check: