Dockerfile expects burrow to already be built

Nobody has claimed this yet.

The Dockerfile seems to expect you to provide the burrow binary, which seems to go against common expectations of portability for a Dockerfile. I could be wrong, but am curious as to why this decision was made? Why not just have the Dockerfile install burrow? If you want to use the iron + binary tactic for size purposes, I would provide both options out of the box.

In the Dockerfile:
```
ADD burrow /app/
```

In addition, the `docker-compose.yml` file mounts the `docker-config` directory to `/etc/burrow`, but the Dockerfile expects you to do that manually. Wouldn't it make more sense to have the `Dockerfile` simply require that you mount your config directory to `/etc/burrow`?

Also, it expects the binary to be lowercase, but it gets installed as uppercase.

For example:
```
FROM golang:alpine3.7
MAINTAINER LinkedIn Burrow "https://github.com/linkedin/Burrow"

RUN apk update
RUN apk add git

RUN go get github.com/linkedin/Burrow
WORKDIR src/github.com/linkedin/Burrow
RUN go install

RUN mkdir /app
WORKDIR /app
RUN mv /go/bin/Burrow ./burrow

CMD ["/app/burrow", "--config-dir", "/etc/burrow"]

```

Inspect Dockerfile and docker-compose.yml first, focusing on the ADD burrow step, the binary name, and the /etc/burrow configuration mount. Compare the requested build and configuration behavior with the current files; done means the documented Docker workflow no longer requires an externally built binary and handles configuration consistently.

Written by the indexing model from the issue text.