Replace ast_manager_publish_message() with a more useful version.

It's much easier to just create a blob of the message.  Convert some AMI events
to use it.

Review: https://reviewboard.asterisk.org/r/2577/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@390268 65c4cc65-6c06-0410-ace0-fbb531ad65f3