function getStackTrace(rows) {
	var stacktrace = '  ---\n';
	var extract = false;
	forEach(rows.split('\n'), function (row) {
		if (!extract) {
			if (row.indexOf('---') > -1) { // start of stack trace
				extract = true;
			}
		} else if (row.indexOf('...') > -1) { // end of stack trace
			extract = false;
			stacktrace += '  ...';
		} else {
			stacktrace += row + '\n';
		}
	});
	// console.log(stacktrace);
	return stacktrace;
}
extract the stack trace for the failed test.
this will change dependent on the environment
so no point hard-coding it in the test assertion
see: https://git.io/v6hGG for example
@param String rows - the tap output lines
@returns String stacktrace - just the error stack part