Prepend the license manifest creation call to ROOTFS_POSTPROCESS_COMMAND
instead of appending to ROOTFS_POSTINSTALL_COMMAND. The latter is not
implemented for the deb backend (and probably ought to just be removed
completely), and by using _prepend we can still ensure it occurs before
package info is removed (and before buildhistory in case it is needed
there in future).
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
