[Piglit] Fix expanding running tests in logger

[Dylan Baker]

This series addresses the problem of the expanding test logger. The
basic problem is that we do some work int he TestResult constructor that
is primarily for use in the summary code, namely converting the string
value of the result into a status.Status object. What happens is that in
the majority of cases the default value is overwritten so this works,
but if a test fails very early in the run it will get passed this
default status, and then the logger will have an assertion error.

This series moves that special code out of TestResult.__init__ into a
secondary constructor which is then used by the path that loads results.

Patch 1 adds a unit test for the problem
Patch 2 fixes the problem
Patch 3 cleanups up a rebase error from the atomic-writes series, this
		is not a series error, but we can throw a bunch of code that
		shouldn't be used (most of which is effectively unreachable at
		this point).