open-iscsi module to manage targets on the initiator.

Follow-up of #3365 as reviewed by @jimi1283

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
- authentication support for the node session
- dis(connects) to given targets
- marks given targets to auto start/connect