Several fixes

 * Avoid settings whitespaces by rewriting whitespace to underscore, since it is forbidden in sensu anyway.
 * I ran into /etc/sensu/conf.d directory does not exist several times for initial setup, so I require package installation for this directory
 * setting subscriber and handler for checks should be optional
  * if handler is an empty array, the server won't process with default handler
  * I don't want to set the handler for all my puppet defined checks, so if I leave it empty, I want to use default handling on server.