scanner integration test fails some times because the test Web server is not multi-threaded
Because the Python Web server used for the integration tests is not multi-threaded, some relays' circuits timeout.
Most of the cases, this is desired since in a public network this would happen too.
It is not desired in the case that the integration test check for a concrete relay measurement success, which is tests/integration/core/test_scanner.py::test_measure_relay_with_maxadvertisedbandwidth (https://travis-ci.org/torproject/sbws/jobs/565274602#L1971).
This case can be solved by checking the descriptor bandwidth, not the measurement.
Ideally, the Python Web server should be changed to be multi-threaded and shutting down some relays for the cases where the tests check failures.