Escaping of command output

Hi,

I've fixed a small problem with the check name sanitizing, and added basic JSON escaping of the command output. (Double quotes in my command's output was causing invalid JSON to be returned.)

I've done this in a very simple way, but a more comprehensive method is given here: http://stackoverflow.com/a/13466143/1011363

However, I didn't want to add a dependency on python to the script.

Regards,
Mike