run-tests: move err file writing to tearDown()

run-tests: refactor testtmp testtmp is now a member variable of our test class. It's value is computed during instance creation and the directory is managed via the lifetime of the test object.

run-tests: store skipped state on Test As code is being moved between functions, we need a member variable to hold skipped state.

run-tests: move some functionality to Test.tearDown()

run-tests: store last result in Test._result Subsequent patches move post-test actions into tearDown(). This requires tearDown() to have access to the last result.

run-tests: report test duration in Test.tearDown()

run-tests: store test return code and output in Test instance A subsequent patch that will introduce tearDown() requires test execution state be stored in the instance.

run-tests: keep track of test start and stop in MercurialTest.run() This brings run() more compatible with unittest.TestCase.run()

run-tests: keep track of test execution state in Test This patch starts a mini series of moving functionality into the newly-established setUp() and tearDown() methods.

run-tests: support setUp() and tearDown() in TestCase wrapper unittest.TestCase.run() calls setUp() and tearDown() during run(). We emulate that implementation.