test_runner: support handling errors from outside of tests

test_runner: give the root test a harness reference

This commit replaces the 'coverage' reference inside of the Test class with a more generic harness reference which includes coverage. This will let the root test more easily track process level state such as code coverage, uncaughtException handlers, and the state of bootstrapping.

test_runner: track bootstrapping process

This commit updates the test harness and root test to track when bootstrapping has completed.

test_runner: throw if harness is not bootstrapped

This commit updates the test harness to re-throw uncaught errors if bootstrapping has not completed. This updates the existing logic which tried to detect a specific error code.

test_runner: handle errors not bound to tests

This commit addresses a previously untested branch of the code. It is possible when using the test runner that an error occurs outside of a test. In this case, the test runner would simply rethrow the error. This commit updates the logic to handle the error in the same fashion as other uncaughtExceptions.