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: http://svn.asterisk.org/svn/asterisk/trunk@390268 f38db490-d61c-443f-a65b-d21fe96a405b