Add Constraints support

Adding constraints support to libraries is slightly more complex than
services as the libraries themselves are listed in upper-constraints.txt
which leads to errors that you can't install a specific version and a
constrained version.

This change adds constraints support by also adding a helper script to
edit the constraints to remove oslo.config.

Change-Id: I98622a0d783aa759e73df4e594afe409ad141bab