fixed the .iso download to work on Mac

wget is not avilable for Mac by default so used curl.

compute_create

@@ -17,7 +17,7 @@ fi
 # Download the ipxe.iso boot image if it doesn't already exist
 if [[ ! -f "$HOME/iso/ipxe.iso" ]]; then
   echo "Downloading the network boot ipxe.iso file"
-  wget -O ~/iso/ipxe.iso http://boot.ipxe.org/ipxe.iso
+  crul -o ~/iso/ipxe.iso http://boot.ipxe.org/ipxe.iso
 fi
 
 VBoxManage createvm --name "$nodename" --register