use best compression on redex builds
use best compression on redex builds

Summary: redex hardcoded the xz compression to level 6 when repacking.  hardcoding to 9 for best compression, but we should also look into respecting the passed in value to the android_binary rule

Reviewed By: dalves

Differential Revision: D5096514

fbshipit-source-id: d45282998da418dcd42bf231203019dd880dcafe

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex