Destroy the generic_monitors container after the core_instances in ccss

For each item in core_instances disposed of in the shutdown of ccss, any
generic monitor instances referenced by the objects will be removed from
generic_monitors during their destruction.  Hilarity ensues if
generic_monitors no longer exists.

Thanks to the Asterisk Test Suite's generic_ccss test for complaining loudly
when it ran into this.
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Merged revisions 374300 from http://svn.asterisk.org/svn/asterisk/branches/10
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Merged revisions 374301 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@374302 65c4cc65-6c06-0410-ace0-fbb531ad65f3