Fix the nic virtual device used by the VM

The default device abstraction caused the network comm to fail during
the load of the kernel image from master.  Changing to the nic type
82540EM fixes the issue.

mk_compute_node

@@ -12,7 +12,7 @@ nodename="$1"
 VBoxManage createvm --name "$nodename" --register
 
 
-VBoxManage modifyvm "$nodename" --memory 2048 --nic1 intnet --intnet1 compute --rtcuseutc on
+VBoxManage modifyvm "$nodename" --memory 2048 --nic1 intnet --intnet1 compute  --nictype1=82540EM --rtcuseutc on
 
 VBoxManage storagectl "$nodename" --name IDE --add ide --controller PIIX4 --bootable on
 VBoxManage storageattach "$nodename" --storagectl IDE --type dvddrive --device 0 --port 1 --medium ~/iso/ipxe.iso