Change graphite queries to comply with the changes made to Graphite data store

As part of PR #28, changes were made to the format in which data is stored in Graphite database so that the data is presented in a user friendly format on the UI. The changes in this PR is to make queries run against Graphite (to send data to Zabbix) to comply with the changes in PR#28.
Just for future spelunkers, `host` here actually a Zabbix-ism (since it thinks we'd alarm on a single host) and is really a service type (e.g. `hbase_master`, `namenode`).