RFC: rc(8) script for bhyve(8) on FreeBSD

Hello,

two years elapsed since I last deployed a FreeBSD machine that utilizd 
bhyve(8), which already had bhyve_config(5) support back then.

I was astonished that I still couldn't find bhyve in /etc/rc.d in 
14.1-stable as of last week.
Since I utilize ng_bridge(8) and do some more things differently than 
vm-bhyve / iocage and the like, I wanted to have something straight 
forward, capable of making use of the wonderful bhyve_config(5) feature, 
for use cases where /usr/share/examples/bhyve/vmrun.sh isn't suitable.

Please find attached my first approch, which currently covers the 
following features:

- auto-preload FreeBSD guest using bhyveload(8) in case config file 
doesn't define lpc.bootrom
- Allows referencing %(youname_somevar) in config file if defined as 
bhyve_youname_somevar in rc.conf(5).
   (For example:
     bhyve_vmdisk_default_pool="myppol2"
     bhyve_vmdisk_default_dataset="bhyveVOL/sys"
     and
pci.0.3.0.path=/dev/zvol/%(vmdisk_default_pool)/%(vmdisk_default_dataset)/%(name) 
in bhyve_config(5) file
   )
- Adaptive handling of start/stop requests depending on 'AUTO' 'ALL' or 
specific list of VM names, depending on the non-bhyve_cfg(5) 'autostart' 
option.
- Hopefully balanced amount of messages about what's going on, to be 
user friendly but not spamming.

There's a lot of room for improvements (selectable pre-jail/post-jail 
order, bootdisk detection, priority handling, a useful 'status' 
implementation, style) and for sure some bugs, but this version works 
well for my current setup.
Happy to contribute if useful for others, feedback welcome.

-harry