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>

* change

* [TD-3986]<test>: modify the subscribe test cases

* [TD-3851]<fix>: taosdemo performance boost.

* change few default values.

* [TD-3851]<fix>: taosdemo performance boost.

change max sql len default value to 1024*1024
Co-authored-by: NShuduo Sang <sdsang@taosdata.com>

* [TD-3968]<fix>: taosdemo data length should be 16*1024

* [TD-3968]<fix>: taosdemo datalen should be 16*1024

fix data buffer issue.

* [TD-3968]<fix>: taosdemo datalen should be 16*1024

commend out unused func for debugging purpose in the future

* [TD-3968]<fix>: taosdemo datalen should be 16*1024

comment off unused function

* [TD-3968]<fix>: taosdemo datalen more than 16k.

comment off unused array.
Co-authored-by: NShuduo Sang <sdsang@taosdata.com>

* [TD-4032]Eliminate false alarms

* update rules

* merge taos-jdbcdriver-2.0.28 all changes to master branch

* change version in cmake/install.inc

* [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-4001]<fix>: taosdemo restful segfault.

due to gethostbyname() is not thread-safe.

* fix uninitialized variable when invalid mode.
Co-authored-by: NShuduo Sang <sdsang@taosdata.com>

[TD-3984]union issues

[TD-3996]udc query issue

* [TD-3985]<fix>: taosdemo timestamp step overflow.

* fix specified subscribe test.

* replace potential overflow of int32 to int64

* replace potential int32 overflow variables to int64.

* replace potential int32 overflow variables to int64.

* change max of int16 to int64 after type changed.
Co-authored-by: NShuduo Sang <sdsang@taosdata.com>

[TD-2039] <test> verify the bug of TD-2039

[TD-3988]add mac test on Appveyor

TD-3948: specify insertion columns after supertable tags

* [TD-3985]<fix>: taosdemo timestamp step overflow.

* fix specified subscribe test.

* replace potential overflow of int32 to int64

* replace potential int32 overflow variables to int64.

* replace potential int32 overflow variables to int64.
Co-authored-by: NShuduo Sang <sdsang@taosdata.com>

[TD-3991]fix client log

* [TD-3985]<fix>: taosdemo timestamp step overflow.

* fix specified subscribe test.
Co-authored-by: NShuduo Sang <sdsang@taosdata.com>

The update contains TD-3983 TD-3912 fixes.

[TD-3921] <test> add case to resolv show streams return erro msg

[TD-3920] <test> add case to fix the bug of TD-3920

[td-3951]<fix>: check the input value of big int which is overflowed.

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

[TD-3940]CQ crash when vnode changes