This is nice in theory, until you need to look at the bootloader status of the
parent, or of a different device entirely. Handle this in plugins for the few
cases we care about and stop setting or clearing IS_BOOTLOADER manually just to
get the vfuncs to be run.
Note: I do not think we want to use cleanup() for attaching devices not in
bootloader states -- as cleanup is only run at the end of the composite update.