add check_script for monitoring connections

Dear jamesc,

we created a new check to allow validation of connections and their states as we do have to ensure that particular users are connected and are actually pushing or receiving messages from/to RabbitMQ. The script is based on the scripts you already provided and were only slightly adjusted (I'm a bad Perl coder..). It's already used in our infrastructure and it works fine. Now I wonder if this script may be of any use for others and whether you mind merging our commit?

Thanks
Mathias