Cleaned up the agument parsing and added support for excluding files/folders.

BUG=angle:552

Change-Id: I0d59f83fe2e20b8bc23564ecfb1f98c08c70ca94
Reviewed-on: https://chromium-review.googlesource.com/187532Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>