OpenTSDBReader任务配置多metric仅读取到第一个metric的原因及解决办法

故障现象：OpenTSDBReader任务配置文件多个metric仅有第一个metric信息可以被读取到
故障原因：OpenTSDBReader类的split方法，在进行task切分的时候首先按照metric进行切分(for循环)，在同一个metric下按照小时进行切分(while循环)的时候，会将配置文件中读取到的beginDateTime进行递增赋值，但是在重新进入for循环时，未将beginDateTime进行复原，导致while循环条件一直为false
解决办法：将DateTime startDateTime = new DateTime(TimeUtils.getTimeInHour(startTime));该行代码放入columns的for循环内的第一行，如下所示：
`//DateTime startDateTime = new DateTime(TimeUtils.getTimeInHour(startTime))；//直接注掉
DateTime endDateTime = new DateTime(TimeUtils.getTimeInHour(endTime));

// split by metric
for (String column : columns) {
DateTime startDateTime = new DateTime(TimeUtils.getTimeInHour(startTime));//修改位置
// split by time in hour
while (startDateTime.isBefore(endDateTime)) {
Configuration clone = this.originalConfig.clone();
clone.set(Key.COLUMN, Collections.singletonList(column));

clone.set(Key.BEGIN_DATE_TIME, startDateTime.getMillis());
startDateTime = startDateTime.plusHours(1);
// Make sure the time interval is [start, end).
// Because net.opentsdb.core.Query.setEndTime means less than or equal to the end time.
clone.set(Key.END_DATE_TIME, startDateTime.getMillis() - 1);
configurations.add(clone);

LOG.info("Configuration: {}", JSON.toJSONString(clone));
}
}`

Start in the OpenTSDBReader class's split method and inspect how startTime is reused across the metric loop and hourly loop. Verify a configuration with multiple metrics produces hourly configurations for every metric, with each metric starting from the original time range.

Written by the indexing model from the issue text.