Aggiunto controllo sull'esistenza dell'immagine del disco anche in vm-start

vm-start

@@ -139,6 +139,12 @@ vbox_attach_medium () {
   local disk_img=$1
   local port_num=$2
   local disk_type=$3
+  # check if disk image exists, otherwise abort
+  if [[ ! -f "${disk_img}" ]]; then
+    echo
+    echo "${ERROR}Disk image ${BOLD}${disk_img}${NORMAL}${ERROR} does not exist on this computer. Abort. Bye!${NORMAL}"
+    exit 0
+  fi
   echo "Attaching disk ${port_num}..."
   VBoxManage modifyhd "${disk_img}" --type ${disk_type}
   vboxmanage storageattach "${VM_NAME}" --storagectl "${STORAGE_CONTROLLER_NAME}" --port ${port_num} --device 0 --type hdd --medium "${disk_img}"