Made DSE raise exceptions instead of log

Previously, when DSE encountered an error when
loading a service, it simply logged the error.

This change raises an error that can be caught.

Currently such errors crash the system, but
in the future the system will respond gracefully
to data service failures.

Change-Id: Iedc66bd9b7e80b567a1012ba879479e5ab6e76f8
Merge "Made DSE raise exceptions instead of log"