RFE: display data from openstack/releases repo

[joelcapitao]

There is data from openstack/releases repo which could be useful in rdopkg.
For instance:

• we could list all project following type: trailing [1] release model. This is useful when preparing RDO release.
• we could compare releases from RDO (Trunk or CBS) repos to latest tag released upstream for each release. We'll be able to spot big gap.

[1] https://github.com/openstack/releases/blob/3d49a8dce3bc9dabdcd6ec4dfda0765f816f07a1/deliverables/wallaby/python-tripleoclient.yaml#L6