docs: def _validate_virtualbox(self):
  
          '''
              a method to validate that virtualbox is running on Win 7/8 machines
  
          :return: boolean indicating whether virtualbox is running
          '''
  
      # validate operating system
          if self.localhost.os.sysname != 'Windows':
              return False
          win_release = float(self.localhost.os.release)
          if win_release >= 10.0:
              return False
  
      # validate docker-machine installation
          from os import devnull
          from subprocess import call, check_output, STDOUT
          sys_command = 'docker-machine --help'
          try:
              check_output(sys_command, shell=True, stderr=STDOUT).decode('utf-8')
          except Exception as err:
              raise Exception('Docker requires docker-machine to run on Win7/8. GoTo: https://www.docker.com')
  
      # validate virtualbox is running
          sys_command = 'docker-machine status %s' % self.vbox
          try:
              vbox_status = check_output(sys_command, shell=True, stderr=open(devnull, 'wb')).decode('utf-8').replace('\n', '')
          except Exception as err:
              if not self.vbox:
                  raise Exception('Docker requires VirtualBox to run on Win7/8. GoTo: https://www.virtualbox.org')
              elif self.vbox == "default":
                  raise Exception('Virtualbox "default" not found. Container will not start without a valid virtualbox.')
              else:
                  raise Exception('Virtualbox "%s" not found. Try using "default" instead.' % self.vbox)
          if 'Stopped' in vbox_status:
              raise Exception('Virtualbox "%s" is stopped. Try first running: docker-machine start %s' % (self.vbox, self.vbox))
  
          return True