configurable working directory for running tests

[accerqueira]

when test runner triggers the run_tests command, it currently looks for a parent directory which contains a test, tests, spec or specs directory, and runs the command there i think it would be nice if you could specify where to run the command, maybe with something like xpath, adapted to filesystem

the default expression would be: ancestor-or-self::directory[directory[matches(@name,"tests?|specs?")]]