Integration test against live system

In order to pin down issues regarding real-world deployments, this merge requests adds an integration test which involve deployed gateways while the bridge is still running on the CI and another test case where bridge and gateway are both remote. Moreover this MR adds an NDT client (https://www.measurementlab.net/tests/ndt/) that tests the throughput in all test cases. It appears that the performance improvements of !36 (merged) are less effective as we hoped.