MFC r271447, r271496
 - Attach the ISO to an ahci-cd emulated device
 - Propagate the error status of /usr/sbin/bhyve

Approved by:re (delphij)
MFC r271934:
Output boot code warning when zpool upgrade -a is used to add features.

PR:		188328
Approved by:	re (marius)
Sponsored by:	Multiplay