piglit not logging stdout

The piglit log files are missing the stdout because it's a bufreader of a pipe and we consumed it all parsing the output.

I've wanted to be able to log stdout from tests before (deqp parse failure debug), maybe the deqp/piglit results parsing should also return a copy buffer of the stdout that had been read in? Or, since the timeoutreader afaik rearms on each read, we could just read all the stdout with timeoutreader in lib.rs and pass the whole buffer in to the parser.