Clearer error informations

[Sjd-Risca]

By now, every time there is a failure error during the inventory generation, only the python error trace and its exceptions are returned. It would be nice if it could be possible to have also a clearer information on what's going on.

For example I'd like to know, if there is a problem like a missing key during an interpolation, a clear error tracing with the following extra informations:

• the interested node
• the interested class
• the missing/wrong key

This would make the debugging of the configuration errors more trivial.

Do you already have some idea in which direction to implement it?