WIP: add explicit exception handling without traceback;

[rhoerbe]

Problem: SATOSA log includes traceback for errors that are sufficiently clear from the error message. Tracebacks are difficult to handle for line-oriented logs and should be eliminated (but this will take time & effort)

This PR introduces SATOSAErrorNoTraceback and bases SATOSAConfigurationError on it.

The satosa_saml_metadata.py script gest extra code to suppress tracebacks.