The first iteration of reader code update to support device removal.
Note, since this update depends more onn memory, the zfsboot/gptzfsboot will
need side work to support proper memory management from libsa.
illumos issue 10166 and review
use zpool remove to remove vdev, then read the pool with loader...
read vim_entries by chunks.
Thank you very much for making this work.
We should get this merged in time for 12.1-RELEASE