Broken double-checked locking implementation

[brettwooldridge]

Did somebody really commit a broken double-checked locking implementation? Come on guys, this is Sophomore year Java...

https://github.com/influxdata/influxdb-java/blob/master/src/main/java/org/influxdb/impl/InfluxDBImpl.java#L311

@jiafu1115

[jiafu1115]

@brettwooldridge do you mean broken is from not support volatile on jdk < 1.5? You can create one PR for it. Thanks