Use serial port for BIOS output

Author: markgoddard

templates/vm.xml.j2

@@ -6,6 +6,7 @@
   <os>
     <type arch='{{ libvirt_vm_arch }}'{% if libvirt_vm_machine is not none %} machine='{{ libvirt_vm_machine }}'{% endif %}>hvm</type>
     <bootmenu enable='no'/>
+    <bios useserial='yes'/>
   </os>
   <cpu{% if libvirt_vm_cpu_mode is not none %} mode='{{ libvirt_vm_cpu_mode }}'{% endif %}>
     <model fallback='allow'/>