Add re-raise argument to start() and cleanup()

To enhance the usability of the Orchestrator class as a reusable
component (e.g., used by WebUI), it should not catch and handle
certain exceptions, without at a minimum re-raising them.

Change-Id: I4ff8320f3a275fbdbe7cf3a21c217f1cf59ddacb
Fixes: bug #1226193
Merge "Add re-raise argument to start() and cleanup()"