Untangle iSCSI authentication code by splitting off the CHAP
implementation.

Reviewed by:	mav@
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation

(cherry picked from commit 1bb0800b27fa08cfe8ed7bc8488ef14bdff2e2a8)
Whitespace fixes.

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation

(cherry picked from commit 853fc00c2a595397930af55fa5123c8e08aa36c0)

Conflicts:
	usr.bin/iscsictl/Makefile
Fix ctld(8) to not show the "auth-group <name> not assigned to any target"
warning for auth-groups assigned to a portal-group.

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Remove misleading statement.  Bump date.

MFC after:	1 month
Sponsored by:	FreeBSD Foundation

(cherry picked from commit d7bc948e22b73d2b3d9f297bd9b268c230973d28)

Conflicts:
	usr.sbin/ctld/ctl.conf.5
Fix ctl.conf example to use proper paths to ZVOLs.

Sponsored by:	The FreeBSD Foundation

(cherry picked from commit 79512487f6d9982d9dadddbb8ffc803c89194160)
Clean up (refactor) discovery a little; no functional changes.

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation

(cherry picked from commit c0426e480a33dc0cee1e988653a3dd620f2a2f8d)