Rename QRFS_* to RS_*

This patch renames QRFS_* to RS_* fields so they can be used in other
places (i.e. LUs) without confusion, as this was initially meant for
query operations.

Signed-off-by: René Nussbaumer <rn@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>