Avoid forcing engine_conf to a dict

It is valid to provide engine_conf that is None and
when a engine is loaded it will notice that it is None
and load its default configuration.

Change-Id: Icde7ac85921f3b434cee39a9dfe7de997f2120bf
Increase the level of usefulness of the dispatching logging

Change-Id: Ief62a3436aa7fe86c98e026ec5522d2f5e2aa29f
Merge "Avoid forcing engine_conf to a dict"
Merge "Increase the level of usefulness of the dispatching logging"