Plumbing for setting own docker registry

* as an operator I can specify an IP to use for docker registry
* as a multi-hypervisor openstack I want to refer back to central
docker registry

Also remove auto-discovery on docker-registry container

Co-Authored-By: Julien Vey <julien.vey@numergy.com>

Change-Id: Iba0e00bda1742aa428b4064bfdb1f80ce1c374c9
Merge "Plumbing for setting own docker registry"
Fix the registry port and ip settings

* The registry ip and port settings were mismatched

Change-Id: I866d39b0f0be39a4a59ca5c6f2550fbf88952a5d
Update babel version and add six module

Change-Id: I2f1c4fa264da095425aabf844b8928e64faf465e
Update README with more specific install/config instructions

This should make installation easier for more casual users.

Also some misc. formatting improvements.

Change-Id: Ifcc9ef9c982ce531787635bb7206b93565998460
Add tempest gate configuration environment variables

These were removed from the openstack-infra nova-docker job
configuration file and moved here so that they can be tweaked without
bother openstack-infra

Change-Id: I77717e119728e65434faff21aceb8ccb5d3e3974
sync'd with upstream