CDRIVER-4645 migrate and run load balancer tests (#1414)

* run simple_http_server.py on port 18000

Port 8000 conflicts with HAProxy started by run-load-balancer.sh in DET

* update load_balancers specification tests

Update to commit https://github.com/mongodb/specifications/commit/5af2ab77a6e68a4528085504ab6bd1360d30a6c8

 to fix test failure when an error is expected.

* use `hello`, not `isMaster` in test failpoint

* add new loadbalanced Evg config

* remove legacy load balanced config

* regenerate Evergreen config

* Sort imports

Co-authored-by: Ezra Chung <88335979+eramongodb@users.noreply.github.com>