Confbridge: add test events for dynamic menus test

Adds a couple of test events for conference menu actions so that it's
easy to discern when those menu actions have been triggered.

(issue ASTERISK-22760)
Reported by: Matt Jordan
Review: https://reviewboard.asterisk.org/r/2999/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@402698 65c4cc65-6c06-0410-ace0-fbb531ad65f3