The results file produced by piglit-run.py contains a serialized
TestrunResult, and the serialization format was horridly homebrew. This
commit replaces that insanity with json.

Benefits:
    - Net loss of 113 lines of code (ignoring comments and empty lines).
    - By using the json module in the Python standard library, serializing
      and unserializing is nearly as simple as `json.dump(object, file)`
      and `json.load(object, file)`.
    - By using a format that is easy to manipulate, it is now simple to
      extend Piglit to allow users to embed custom data into the results
      file.

As a side effect, the summary file is no longer needed, so it is no longer
produced.

Reviewed-by: Paul Berry <stereotype441@gmail.com>
Signed-off-by: Chad Versace <chad@chad-versace.us>