Add qpid-python to requirements

Qpid is a supported messaging library, and without this it is
necessary to install it manually in order to use Qpid in some
environments, notably the one used by TripleO.

Change-Id: I398c1d35295223cbc6969b386129c6fc9acbefc7
Closes-Bug: #1225191
Merge "Add qpid-python to requirements"