Do not hardcode the list of VM's to start inside the bhyvevm script.

Introduce two variables which must be placed in /etc/rc.conf:
  bhyvevm_list
  bhyvevm_${VMNAME}_conf

For example, if the following entries are in /etc/rc.conf:
  bhyvevm_list="vm1 vm2"
  bhyvevm_vm1_conf="/vm/vm1.conf"
  bhyvevm_vm2_conf="/vm/vm2.conf"

Then for each entry in bhyvevm_list, the corresponding VM
will be started/stopped with the config file specified
by bhyvevm_${VM}_conf.