Introduce open-iscsi module to manage targets on the initiator.

New module to manage iscsi "client side": (dis)connect to targets on the initiator.
- based on the Linux open-iscsi software
- performs a discover and updates the local persistent database
- returns available nodes/targets for a given iscsi portal
- dis(connects) to given targets
- marks given targets to auto start/connect

As I don't use this at $WORK, and couldn't test these features, I didn't implement these yet:
- authentication - but should be trivial to add