exceptions during fixture detail gathering mask original exception

[Robert Collins]

If a fixture errors when we attempt to gather its details, the result can be that we don't show the original exception. This is (needless to say) bad.

https://bugs.launchpad.net/nova/+bug/1330763 is where this was observed.

[Robert Collins (lifeless)]

        try:
            fixture.setUp()
        except:
            gather_details(fixture.getDetails(), self.getDetails())
            raise

is the culprit - note that we don't gather exceptions from gather_details.