import_lab()
This PCL function imports an existing topology from a string. With the new
schema and the use of UUIDs which was introduced in 2.3, the export format of
labs has also changed:
- interfaces are now stored with the nodes and not in a global list anymore
- specific attributes of nodes/interfaces are not stored in a "data" dictionary
anymore but with the node/interface itself
Importing / exporting such a lab will use the new representation. Going
forward, the backward compatibility will be removed with 2.5. At the moment,
deprecation warnings will be printed in these cases.