Change how realms are handled for outbound authentication.

With this change, if no realm is specified in an outbound auth
section, then we will simply match the realm that was present
in the 401/407 challenge.

(closes issue ASTERISK-22471)
Reported by George Joseph
(closes issue ASTERISK-22386)
Reported by Rusty Newton

Patches:
	outbound_auth_realm_v4.patch uploaded by George Joseph (License #6322)
........

Merged revisions 399059 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@399082 65c4cc65-6c06-0410-ace0-fbb531ad65f3