This enables booting interactive GRUB menus (e.g. install CDs) with
libvirt-bhyve.

Caveat: A terminal other than the '--console' option to 'virsh start'
(e.g. 'cu -l /dev/nmdm0B -s 115200') must be used to connect to
grub-bhyve because the bhyve loader path is synchronous and must occur
before the VM actually starts.

Changing the bhyveProcessStart logic around to accommodate '--console'
for interactive loader use seems like a significant project and probably
not worth it, if UEFI/BIOS support for bhyve is "coming soon."