Better instance fault message when rescheduling.

The old code would use exc_info[0] which is the type of exception, not
the exception itself. This would result in the `message` attribute
always being 'type' and the first-line of details being useless.

The solution is to pass the actual exception object so that `message`
becomes the class-name and the first-line of details becomes the `repr`
of the exception object.

Fixes bug 1100559

Change-Id: Ibaeb5dc5af419de6c98b44aec07bff225b2f9956
Merge "Better instance fault message when rescheduling."