docs: def clear(mnt):
      '''
      Pass in the mnt dict returned from nbd_mount to unmount and disconnect
      the image from nbd. If all of the partitions are unmounted return an
      empty dict, otherwise return a dict containing the still mounted
      partitions
  
      CLI Example:
  
      .. code-block:: bash
  
          salt '*' qemu_nbd.clear '{"/mnt/foo": "/dev/nbd0p1"}'
      '''
      ret = {}
      nbds = set()
      for m_pt, dev in six.iteritems(mnt):
          mnt_ret = __salt__['mount.umount'](m_pt)
          if mnt_ret is not True:
              ret[m_pt] = dev
          nbds.add(dev[:dev.rindex('p')])
      if ret:
          return ret
      for nbd in nbds:
          __salt__['cmd.run']('qemu-nbd -d {0}'.format(nbd), python_shell=False)
      return ret