updated proxy.go to include hostname as a column rather than a series pr...

...efix

@hoonmin - Thanks for writing this proxy! It's much more reliable than some others I've tried.

Would you be interested in this change to include the hostname as a column to each time series, rather than as a prefix to each series?

In my testing, I've found that InfluxDB is more performant when there are fewer time series to manage. Grouping similar metrics into a single series with a distinguishing field (such as hostname) yields better query performance, usually.

So far this change is working locally and handling metrics just fine, but let me know if I did anything you don't like. :-)