[TD-4037]<test>: add taodemo-testcase that childtable_count is less than or equal zero and num_of_records_per_req  is  equal zero

By this commit, It will close TD-3639.

It will not require test case to write *correct* datetime string to pass
a test case. One test could use seconds, milliseconds or microseconds to
check data.

That means the three tests are equivalent:

```python
.checkData(0, 0, "2020-01-01 00:00:00")
.checkData(0, 0, "2020-01-01 00:00:00.000")
.checkData(0, 0, "2020-01-01 00:00:00.000000")
```
Co-authored-by: NHuo Linhe <linhehuo@gmail.com>

* [TD-4032]Eliminate false alarms

* update rules

* [TD-4025]<fix>: travis ci broken due to valgrind dependency missed.

* [TD-4025]<fix>: travis ci broken due to valgrind dependency missed.

change focal to bionic.

* [TD-4025]<fix>: travis ci broken due to valgrind dependency missed.

install python3.8

* [TD-4025]<fix>: travis ci broken due to valgrind dependency missed.

install python3.8 and pip, setuptools

* [TD-4025]<fix>: travis ci broken due to valgrind dependency missed.

install python3.8, and install pip and setuptools

* [TD-4025]<fix>: travis ci broken due to valgrind dependency missed.

modify smoketest.sh to python3.8
Co-authored-by: NShuduo Sang <sdsang@taosdata.com>

* [TD-3906]<fix>: taosdemo back to 4 INT columns.

* [TD-3906]<fix>: taosdemo back to 4 columns.

test case need change correspondingly.
Co-authored-by: NShuduo Sang <sdsang@taosdata.com>

* [TD-3401]<fix>: taosdemo query statistic.

refactor func name.

* [TD-3401]<fix>: taosdemo query statistic.

refactor func name 2.

* [TD-3401]<fix>: taosdemo support query statistic.

implementation.

* cleanup
Co-authored-by: NShuduo Sang <sdsang@taosdata.com>

patch for master.
Co-authored-by: NShuduo Sang <sdsang@taosdata.com>