run-tests: move env into Test
Environment variables are an implementation detail of how tests are
executed. This patch moves environment variable logic into Test and
completely hides it from the outside.
With this patch, a Test can be executed with two lines: init + run().
Tests are still single-use and take a more arguments to the constructor
than likely necessary. These will get addressed in subsequent patches.
run-tests: move killdaemons into Test.run()
killdaemons() was the only part of runone() looking at env variables. We
move killdaemons() into Test.run() to enable us to fully move env into
Test.