Parse alert timestamp, return UTC datetime object to maintain Python 2 compatibility.

def _ts_parse(ts):
    """Parse alert timestamp, return UTC datetime object to maintain Python 2 compatibility."""
    dt = datetime.strptime(ts[:19],"%Y-%m-%dT%H:%M:%S")
    if ts[19] == '+':
        dt -= timedelta(hours=int(ts[20:22]),minutes=int(ts[23:]))
    elif ts[19] == '-':
        dt += timedelta(hours=int(ts[20:22]),minutes=int(ts[23:]))
    return dt.replace(tzinfo=pytz.UTC)