Fix masking of fixture.setUp errors.

Exceptions in a ``fixture.getDetails`` method will no longer mask
errors raised from the same fixture's ``setUp`` method.
(Robert Collins, #1368440)

Change-Id: I39da334ba57683fd71a5d7af16c32d9170f6e626
Merge pull request #105 from rbtcollins/bug-1368440

Fix masking of fixture.setUp errors.