Report to console when an bootloader has been specified but not available.

[tatuzemdp]

Report consoling when an bootloader has been specified but not installed. this can be seen on the logs but will be nice to just tell it louder on the console output. Also will be great to have a "vm log $vmnam$"

[cgull]

I also had a similar problem today, but with UEFI images-- the system didn't have the uefi-edk2-bhyve* packages installed, and I had configured UEFI boot on a VM. vm console -i <vmname> exited immediately after starting. This is logged in the VM's log too, so it didn't take long to find the root cause.