Fix the job set required for Rocky

Horizon in Rocky will only support Django 1.11 and 2.0.
Also, Horizon is trying to be more compatible with Python 3.
See: https://blueprints.launchpad.net/horizon/+spec/django2-support

This require few changes (for master only):
- remove the jobs and the tox entry points for unit tests
  with Django < 1.11 (which started to fail anyway after some
  recent changes in Horizon);
- add a tox target and a corresponding non-voting job which runs
  the unit tests using Django 2.0 with Python 3;
- create a basic job for all non-standard unit tests jobs (even if
  there is just one right now) which improves the set of irrelevant
  files (translations, release notes, documentation).

Change-Id: I8d87fb3bcdb1baa221246ca4fc5edf8ae14f0cb2

.zuul.yaml

@@ -1,26 +1,22 @@
 - project:
     check:
       jobs:
-        - sahara-dashboard-tox-py27-dj19
+        - sahara-dashboard-tox-py35dj20:
-        - sahara-dashboard-tox-py27-dj110:
             voting: false
-            branches: ^(?!stable/ocata).*$
-    gate:
-      jobs:
-        - sahara-dashboard-tox-py27-dj19
 
 - job:
-    name: sahara-dashboard-tox-py27-dj110
+    name: sahara-dashboard-tox-base
-    parent: tox
+    parent: openstack-tox
     required-projects:
       - openstack/horizon
-    vars:
+    irrelevant-files:
-      tox_envlist: py27dj110
+      - ^.*\.rst$
+      - ^doc/.*$
+      - ^releasenotes/.*$
+      - ^sahara_dashboard/locale/.*$
 
 - job:
-    name: sahara-dashboard-tox-py27-dj19
+    name: sahara-dashboard-tox-py35dj20
-    parent: tox
+    parent: sahara-dashboard-tox-base
-    required-projects:
-      - openstack/horizon
     vars:
-      tox_envlist: py27dj19
+      tox_envlist: py35dj20

tox.ini

@@ -31,20 +31,9 @@ commands = flake8
 [testenv:venv]
 commands = {posargs}
 
-# Django-1.8 is LTS
+[testenv:py35dj20]
-[testenv:py27dj18]
+basepython = python3.5
-basepython = python2.7
+commands = pip install -U --pre django
-commands = pip install django>=1.8,<1.9
-           /bin/bash run_tests.sh -N --no-pep8 {posargs}
-
-[testenv:py27dj19]
-basepython = python2.7
-commands = pip install django>=1.9,<1.10
-           /bin/bash run_tests.sh -N --no-pep8 {posargs}
-
-[testenv:py27dj110]
-basepython = python2.7
-commands = pip install django>=1.10,<1.11
            /bin/bash run_tests.sh -N --no-pep8 {posargs}
 
 [testenv:py27integration]