'Given raw output for the df command, transform it into a normalized
list devices. A \'device\' is a list with fields corresponding to the
output of df output on each platform.'

def _list_devices(self, df_output):

    all_devices = [l.strip().split() for l in df_output.splitlines()]
    raw_devices = [l for l in all_devices[1:] if l]
    flattened_devices = self._flatten_devices(raw_devices)
    return [d for d in flattened_devices if self._keep_device(d)]
