Allow nesting BaseHandler exception handler decorators.
    
    Previously, when multiple decorated methods were nested and
    one of them raised an exception, the exception has been handled
    by all the decorators.
    
    This is not right way, because exception which should be handled
    just by the `fail_artifact_build_on_handler_exception` decorator
    was later re-raised and handled also by the `fail_event_on_handler_exception`
    making the `fail_artifact_build_on_handler_exception` useless in this
    combination of decorators.
    
    This commit fixes this by changing the decorators to handle the
    exception only once. That means only the first decorator will
    handle the exception.