Update `How to run the tests` section
Update `How to run the tests` section

Added note how to run integration tests and updated supported
Django versions.

Change-Id: I0edff1da161b27e060b13dda2ef3f98ad5ee58e1

openstack/horizon,openstack/horizon,openstack/horizon,ChameleonCloud/horizon,ChameleonCloud/horizon,openstack/horizon,ChameleonCloud/horizon,ChameleonCloud/horizon