preparation for configurable name of cuttlefish conf files

In order to make cuttlefish accept a conf filename as a configuration parameter, I needed to add a default which is not `riak.conf`. it's `cuttlefish.conf`. Anyway, if this lands in riak first, it won't be an issue.

Also, I figured out that I didn't need the cuttlefish plugin in the main rebar.config, only the one in rel.