bhyve VM Support

[gronke]

FreeBSD 12 has support for jailed bhyve VMs, see https://reviews.freebsd.org/D16057

The configuration option allow_vmm (as used by iocage/iocage) is inviting because the manual configuration requires changes to devfs_rules and jail parameters.

1. A ZFS volume
2. A null-modem device (nmdm(4))
3. UEFI GOP (no devfs rule, but IP assigned to the jail)
4. A tap device

devfs_rules.conf

[devfs_rules_bhyve_jail=25]
add include $devfsrules_jail
add path vmm unhide
add path vmm/* unhide
add path tap* unhide
add path zvol/tank/bhyve/* unhide
add path nmdm* unhide

jail parameters

allow.vmm: 1
ip4.addr: <IP4Address>

[igalic]

how do we test this?