The max size of pServer->label plus i can be 18, which exceeds
pThread->label, though we are not likely to have so much threads.

* [TS-498]<test>: add a test case for HttpClientPoolUtil

* [TS-498]<fix>: fixed 'no sql input' bug

* throw exception when httpEntity is null

* [TS-498]<fix>: change taosd keepAlive to 30s
Co-authored-by: Nxywang <xywang@taosdata.com>

* [TS-498]<test>: add a test case for HttpClientPoolUtil

* [TS-498]<fix>: fixed 'no sql input' bug

* throw exception when httpEntity is null

* [TS-498]<fix>: alter Keep Alive Time in RESTful pool
Co-authored-by: Nxywang <xywang@taosdata.com>