Make hints for invalid SIP devices return Unavail, not idle

This patch drastically simplifies the device state aggegation code.
The old method was not only overly complex, but also made it impossible
to return AST_DEVICE_INVALID from the aggregation code. The unit test
update is as a result of fixing that bug.

The SIP change stems from a bug introduced by removing a DNS lookup
for hostname-based SIP channels.

(closes issue ASTERISK-16702)
Review: https://reviewboard.asterisk.org/r/1808/
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Merged revisions 358943 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 358944 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@358945 65c4cc65-6c06-0410-ace0-fbb531ad65f3