To quickly answer the question of "how much data is a UID using?" we
need a GID range to label files on external storage, similar to
the GID ranges already defined for cached and shared data.
Also define a new GID that will be used to label the OBB files shared
between all users under /data/media/obb.
Test: builds, newly added tests pass
Bug: 34263266
Change-Id: I16fb7d166c3dcdeafbf477162d191d3b73ae8ac2