multi graphite pickle should be good like "multi graphite" one

We collect many metrics from a server and send metrics directly to two different graphite servers in different sites.

We're using pickle because we collect so many metrics from each server.

Actually our need and my paths is very similar to #328, I've just copied and changed th contents of multigraphite, maybe it should be better if we use same solution with the mongodb one as in aec83bb53ad7b9bde4b6e78643d3e4f51d215e49 (one handler with "host" and "hosts" config parameters instead of introducing new Multi* handlers).

But I'm not sure about breaking the backward compatibility, so I've just added a new handler for now.