Add find_fastest_apt_source.sh (#2342)
Add find_fastest_apt_source.sh (#2342)

* Add find_fastest_apt_source.sh

for building the `sqlflow:dev` and `sqfllow:ci` Docker images.

* Make it exectuable

* Remove two sites that are not mirrors
sql-machine-learning/sqlflow,sql-machine-learning/sqlflow,sql-machine-learning/sqlflow,sql-machine-learning/sqlflow,sql-machine-learning/sqlflow,sql-machine-learning/sqlflow