Rejig dogstatsd config

[noqcks]

Currently, kvexpress says that dogstatsd config is available through --dogstatsd_address but this is not true, since godspeed.NewDefault() uses the default statsd host/post.

This PR parses DogStatsdAddress into Host and Port for use w/ godspeed.New() to setup statsd host and port.

I chose to leave DogStatsdAddress as an entrypoint rather than creating new cli options for host and post so as to be backwards compatible.

[brandon-dd]

Looks like there's a commands/config_test.go file as well, maybe adding a lil something there to (for example) make sure the parsing works as you expect would be good?

[bonnefoa]

nitpick: you could get rid of the DogStatsdAddress variable and directly check for DogStatsdHost instead
Otherwise, looks good to go