devtool: allow passing service host as optional arg, `svchost` (#949)
devtool: allow passing service host as optional arg, `svchost` (#949)

* allow passing service host other than the default, `127.0.0.1` as optional arg, `svchost`
* necessary for container orchestration tools such as `docker-compose` and `kubernetes`

relates-to: #919 
livepeer/go-livepeer,livepeer/go-livepeer