* [TD-4752]<feature>: python connector support nanosecond.

* [TD-4752]<feature>: support nanosecond in test framework.

return integer for nanosecond in connector since python does not support nanosecond yet.

* [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

* fix timezone build error with clang/linux.

* change fixed version python 3.8 to 3.
Co-authored-by: NShuduo Sang <sdsang@taosdata.com>