Return the timezone in /etc/adjtime of the system clock

def _get_adjtime_timezone():
    '''
    Return the timezone in /etc/adjtime of the system clock
    '''
    adjtime_file = '/etc/adjtime'
    if os.path.exists(adjtime_file):
        cmd = ['tail', '-n', '1', adjtime_file]
        return __salt__['cmd.run'](cmd, python_shell=False)
    elif os.path.exists('/dev/rtc'):
        raise CommandExecutionError(
            'Unable to get hwclock timezone from ' + adjtime_file
        )
    else:
        # There is no RTC.
        return None