Reverted: loader: allow booting from pool with log device

Apparently people are using log with boot pool, so we can not just
error out there. Still we will need to investigate how to handle
log properly.

(cherry picked from commit f331eb7d346b5e6b33b7e180fc876bfd853ba6ef)
(cherry picked from commit ae3f74e7638b91bdc778fbaee9caeab917190a82)