Merge with OpenStack requirements

This unifies the pip/test-requires with the common requirements
defined in the OpenStack/requirements repository, which simplifies
dependency tracking for packaging purposes. There are small
minimum-required version bumps that most likely make sense for
horizon as well (or are already implicitely required due to transitive
dependencies).

Change-Id: I50d7d72b54a95012eb7a4f350ef0c3ef88047e01
Merge "Merge with OpenStack requirements"