tests: make test-serve works on system that allow user to bind low port It is possible to encounter linux system configured in a way that allow port < 1024 to be bound by any users. So we update a test to focus more on the actual test: "resolving `daytime` to an actual port number. The new auto-scaling CI runner provided by clever cloud is doing so. This is the initial motivation for this change, but it seems useful anyway. Differential Revision: https://phab.mercurial-scm.org/D11228