run-tests: capture execution results in a TestResult class Some implementation details of test execution still live outside of Test. These include determining what a result means and cleaning up after the test. To move to the world where more of this logic can live inside Test or a derived object, the logic for test execution needs to be refactored. Specifically, exception trapping and opportunities for result processing need to be moved into Test. This patch starts the process by establishing a TestResult class for holding the results of a test execution. In order to actually use this class, exception trapping and execution time recording needed to be moved into Test.run().