dEQP: Add case file generator script. Use the dEQP null platform for speed and to avoid popping up a new window. Store the case lists as .gz files to save space in the repo. BUG=angleproject:998 Change-Id: Ib9b10b8a83edc510cc98f120847b1cf93a3d2f78 Reviewed-on: https://chromium-review.googlesource.com/273975 Reviewed-by: Zhenyao Mo <zmo@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>