Adapt esp8266 tests to use a test harness

[neophiliac]

Using a test harness reminds the test developer of the three parts to a good test (consistent starting state, event to inject, measurable result state), and allows the possibility of automation which could be as simple as a shell script or make target or as complex as a CI pipeline. It also makes it easier to build more tests as needed.

This feature will be complete when all existing tests give the same result as they do now when run under the test harness.