Currently, sending SIGTERM to the bhyve process triggers ACPI poweroff
for a VM. However, when running bhyve in monitor mode (-M), there are
two processes: the monitor process and the actual VM process. Sending
SIGTERM to the VM process works as before -- it powers off the VM.
But sending SIGTERM to the monitor process just kills the monitor process,
leaving the stale VM process running.
Thus, forward the SIGTERM signal from the monitor process to the
VM process for consistency.