Comment 1 for bug 1510575

All of the libs that are found within the global-requirements.txt within https://github.com/openstack/requirements are built within the repo server environment. Within the build process the lookup plugin is used to see what packages are being used throughout the stack, that data is then compared to the global requirements and a difference is generated. All of the requirements files are built using one of two pip build tasks that leverage a constraints file to provide boundaries for the build process.

The output of a build can be found here:
http://rpc-repo.rackspace.com/os-releases/12.0.0/requirements_local_filtered.txt
http://rpc-repo.rackspace.com/os-releases/12.0.0/requirements_global_requirements.txt
http://rpc-repo.rackspace.com/os-releases/12.0.0/requirements_constraints.txt

Within that build process an absolute requirements file is generated which will allow a deployer to create all of the base requirements as needed at anytime:
http://rpc-repo.rackspace.com/os-releases/12.0.0/requirements_absolute_requirements.txt

All of that leads me to the question of, what alternative lib, thats not part of upstream, are we not already building?

As an aside, you could add additional deps to the global-requirement-pins.txt which would load additional packages / pins into the build / constraint process.
* https://github.com/openstack/openstack-ansible/blob/master/global-requirement-pins.txt

That said it may be a good idea to scan /etc/openstack_deploy (as you've mentioned) for additional packages / pins. The plugin already loads in using a list and should be a trivial matter to extend however its never been tested with more than one source. If that's something that you wouldn't mind taking on I'd be for supporting that as an extension for further flexibility.