Drop old django tests
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

openstack/horizon,openstack/horizon,openstack/horizon,NeCTAR-RC/horizon,noironetworks/horizon,NeCTAR-RC/horizon,ChameleonCloud/horizon,NeCTAR-RC/horizon,ChameleonCloud/horizon,noironetworks/horizon,openstack/horizon,noironetworks/horizon,ChameleonCloud/horizon,ChameleonCloud/horizon,NeCTAR-RC/horizon,noironetworks/horizon