Allow specifying additional tests for service config as a string

This is kind of a hack since it takes a plain string and includes it without proper validation, but the monit config format is too complex to represent as a hash and can't be easily validated. Making a resource with multiple templates a-la https://github.com/netmanagers/puppet-nginx/blob/master/manifests/resource/vhost.pp would be possible, but that seems a little excessive to me. 

Reference for monit config: http://mmonit.com/monit/documentation/monit.html#service_tests