isns: Add docs for deregistering discovery domains.

Without this update to the isnsadm help message and
man page, it can be difficult to figure out how to
deregister a registered discovery domain.
Added new utility script to generate initiator name

Signed-off-by: Lee Duncan <lduncan@suse.com>
Added new util script to aid in CNA setup

Signed-off-by: Lee Duncan <lduncan@suse.com>