Allow keeping the app open after tests complete. Send a notification with test results.
Unregister the console listener in cleanup if necessary to allow reuse of the test harness.
Merge pull request #1590 from Mossop/mochitestification-2

Bug 1035512: SDK pieces for mochitests. r=erikvold.

This allows the test harness to be kept open after tests complete so we can run add-on tests in the same runtime. It also cleans up consoleListener properly if we want to re-use the test harness in a single loader.