Drop old django tests

django 1.8 to 1.10 are incompatible with django 2.0.
We only supports Django >= 1.11 in Rocky and UTs with
Django <= 1.10 are no longer needed.

Conditions using django.VERSION will be dropped in a later patch
only because moving them to this patch causes many merge conflicts.

blueprint django2-support
Change-Id: I0611297e70d8e58d53e94635b0b7175d94df195b

.zuul.yaml

@@ -9,24 +9,6 @@
       - ^openstack_dashboard/locale/.*$
       - ^openstack_auth/locale/.*$
 
-- job:
-    name: horizon-openstack-tox-py27dj18
-    parent: horizon-openstack-tox-base
-    vars:
-      tox_envlist: py27dj18
-
-- job:
-    name: horizon-openstack-tox-py27dj19
-    parent: horizon-openstack-tox-base
-    vars:
-      tox_envlist: py27dj19
-
-- job:
-    name: horizon-openstack-tox-py27dj110
-    parent: horizon-openstack-tox-base
-    vars:
-      tox_envlist: py27dj110
-
 - job:
     name: horizon-openstack-tox-py35dj20
     parent: horizon-openstack-tox-base
@@ -72,17 +54,11 @@
 - project:
     check:
       jobs:
-        - horizon-openstack-tox-py27dj110
-        - horizon-openstack-tox-py27dj19
-        - horizon-openstack-tox-py27dj18
         - horizon-openstack-tox-py35dj20:
             voting: false
         - horizon-selenium-headless
         - horizon-dsvm-tempest-plugin
     gate:
       jobs:
-        - horizon-openstack-tox-py27dj110
-        - horizon-openstack-tox-py27dj19
-        - horizon-openstack-tox-py27dj18
         - horizon-selenium-headless
         - horizon-dsvm-tempest-plugin