Low: RA: iSCSITarget, iSCSILogicalUnit: rename instance attributes

This patch renames some resource parameters (a.k.a. supported instance
attributes) as discussed on the mailing list:

• "params" -> "additional_parameters" (so as not to conflict with the CRM shell's "params" keyword, and to also distinguish from other, named parameters that can be set via individual instance attributes).

• "initiators" -> "allowed_initiators" (to remove ambiguity)