Bug in "ns" precision when updating influxDB with string format of time

[xinlongxu]

Floating point calculation cause difference record when updating with string format of time.

"2018-12-19T05:33:59.999Z" is the raw time of string format
"2018-12-19T05:33:59.999000064Z" is the new time record when updating with the above time, but insert a new record

That happened becouse of the floating point calculation in line_protocal.py

def _convert_timestamp(timestamp, precision=None):
    if isinstance(timestamp, Integral):
        return timestamp  # assume precision is correct if timestamp is int

    if isinstance(_get_unicode(timestamp), text_type):
        timestamp = parse(timestamp)

    if isinstance(timestamp, datetime):
        if not timestamp.tzinfo:
            timestamp = UTC.localize(timestamp)

    ns = (timestamp - EPOCH).total_seconds() * 1e9

        if precision is None or precision == 'n':
            return ns
        elif precision == 'u':
            return ns / 1e3
        elif precision == 'ms':
            return ns / 1e6
        elif precision == 's':
            return ns / 1e9
        elif precision == 'm':
            return ns / 1e9 / 60
        elif precision == 'h':
            return ns / 1e9 / 3600

    raise ValueError(timestamp)

[clslgrnc]

Duplicate of #649?

[xginn8]

Closing as duplicate of #649