DRMAA_ERRNO_NO_RUSAGE ignore on wait

On wait method, if method returns DRMAA_ERRNO_NO_RUSAGE, value is considered as an error.

This is a valid value, application simply consider there is no available usage data.

It's considered an error because it's an error code, and returned as such by the C API. It is a bit strange that we don't have a more specific exception type for that error though, and instead just raise a generic DrmException.