Process events even without 'id' in them

This was breaking syndic matching.  The syndic would return its list of
expected minions, but that event does not have 'id' in it.  Thus, the
master would not process that event and it would either result in huge
delays for minion returns or the returns for minions under syndics
wouldn't appear at all on the CLI.
Add doc for `syndic_wait` config option
Merge pull request #8335 from basepi/syndic7671

Fix for matching minions under syndics