message: 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
diff: @@ -442,7 +442,7 @@ class XZSDexMode(BaseDexMode):
  for x in abs_glob(dex_dir, self._store_name + '-*.dex.jar'))
  # XZ-compress the result
  - subprocess.check_call(['xz', '-z6', '--check=crc32', '--threads=6',
  + subprocess.check_call(['xz', '-z9', '--check=crc32', '--threads=6',
  concat_jar_path])
  # Copy all the archive and metadata back to the apk directory
  