Draft: Add direct lustre api calls

Add lustre api calls to scan OSTs for their sizes and add a call to create a file with a given stripe.

Needs more testing, but the OST scan works. That gets the used size but not whether the OST can be written to. That information is not available to clients. To work around that we can request the assigned OST of the file, this will change if the OST is not available.

As well as a scan a sorted cull of OSTs based on the free space is provided. Using that we can prefer empty OSTs first and avoid overfilling unless we are over committed.

TODO: make use of the more advanced OST knowledge, especially when working over MPI.