Boot using BIOS from /etc/firmware/vmm-bios by default.

Instead of using the internal "vmboot", VMs will now be booted using
the external BIOS firmware in /etc/firmware/vmm-bios (which is subject
to a LGPLv3 license).  Direct booting of OpenBSD kernels or
non-default BIOS images is still supported for now using the -b/boot
option that is replacing the -k/kernel option.
As requested by Theo, vmd(8) fails if neither the default BIOS is
found nor a kernel has been specified in the VM configuration.  The
"vmm" BIOS has to be installed using fw_update(1), which will be done
automatically in most cases where the OpenBSD can fetch it after
install/upgrade.
OK mlarkin@

src/etc/examples/vm.conf

@@ -1,4 +1,4 @@
-# $OpenBSD: vm.conf,v 1.6 2016/10/05 18:01:52 reyk Exp $
+# $OpenBSD: vm.conf,v 1.7 2017/03/25 16:28:25 reyk Exp $
 
 #
 # Macros
@@ -24,8 +24,7 @@ switch "local" {
 
 # OpenBSD snapshot install test
 vm "openbsd.vm" {
-	memory 512M
-	kernel $sets "bsd.rd"
+	boot $sets "bsd.rd"
 
 	# First disk from 'vmctl create "/home/vm/OpenBSD.img" -s 4G'
 	disk "/home/vm/OpenBSD.img"
@@ -42,7 +41,6 @@ vm "openbsd.vm" {
 vm "vm1.example.com" {
 	disable
 	memory 1G
-	kernel "/bsd"
 	disk "/home/vm/vm1-disk.img"
 
 	# Use a specific tap(4) interface with a hardcoded MAC address