Improved celestial dynamics test

Description

The celestial dynamics is now a multisystem simulation with loops over the systems. Namespaces are now obtained from the input file, and the operations are now done by looping over the systems. At the moment all possible interactions between systems are used, as we don't have yet an input system to define the interactions in a generic way.

A bug is fixed for the exist condition of the global propagation loop.

Is blocked by !791 (merged).

News snippet

The celestial dynamics is now a multisystem simulation with loops over the systems.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.