Document MissingParams error message for /ari/events

git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@393749 f38db490-d61c-443f-a65b-d21fe96a405b
Print error details when set nonblock fails

git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@393757 f38db490-d61c-443f-a65b-d21fe96a405b