[Piglit] Fix bugs in recent summary changes

[Dylan Baker]

This series fixes 3 bugs in the recent summary changes. There is a
fourth bug reported by Ilia regrading skip in regressions, which I have
confirmed and am investigating. However, I have these 3 patches done,
which fix problems, and I thought I would send them out sooner rather
than later.

Patch 1: Fixes a unit test. It served it's purpose as-is, but this
         changes makes the test better
Patch 2: Fixes odd results in tests with subtests
Patch 3: Fixes html summaries that compare two results with differing
         subtests
Patch 4: Fixes a bug which leaves command out of the json results.