code: def _dusty_vm_exists():
      
      existing_vms = check_output_demoted(['VBoxManage', 'list', 'vms'])
      for line in existing_vms.splitlines():
          if '"{}"'.format(constants.VM_MACHINE_NAME) in line:
              return True
      return False
docs: We use VBox directly instead of Docker Machine because it
      shaves about 0.5 seconds off the runtime of this check.