Bug 860516 - Extract the filter for each harness.

This patch extract the filter phase out of the harness function.  The filter phase is then reuse in a standalone phase to produce the data structure expected by the submitter out-of a shell-like output.

That way, running benchmarks on B2G and providing the same shell-like output makes things easier for humans to check, and for tools to process (without adding yet another input format).