ZFSSA iSCSI driver cannot add multple initiators to a group

All initiators defined in zfssa_initiator property would be
added to the group.
Also fixed some typos related to initiators error messages.

Change-Id: Iec6c90702e5aafa153b4a7f1e429974ac450afc0
Closes-Bug: #1369750
(cherry picked from commit f94d671e627dd7b5143422ffe739418fcfb51a70)
Merge "ZFSSA iSCSI driver cannot add multple initiators to a group" into proposed/juno