Add dirac_add_files method for the Rucio/Dirac integration

[cserf]

Motivation

The goal of the method is to have a atomic way to create files for Dirac. Use case : I would like to create a file named /belle//user/serfon/dir/mytest.root. This should be part of dataset /belle/user/serfon/dir. The method needs to :

• Check if /belle/user/serfon/dir and all it's ascendants /belle/user/serfon, /belle/user, etc. exist. If not it creates and attachs them.
• Create the file+replicas and a rule on the dataset.

Modification

Create a new client, REST, API, core for dirac methods

[mlassnig]

Don't we have something like this for ATLAS Tier-0 already?

[cserf]

Nope. T0 just does a only add_replicas + attach and it's not atomic. What we want here is different, because we need to reconstruct the hierarchical namespace :
Container /belle containing container /belle/user (and so on) containing dataset /belle/user/serfon/dir containing file /belle//user/serfon/dir/mytest.root . The method should be able to create any of the non existing directories in an atomic way.