Show user friendly address to reach the coordinator

[ewoutp]

fixes #23

Sample output

2017/04/18 07:19:36 dbserver up and running.
2017/04/18 07:19:37 coordinator up and running.
2017/04/18 07:19:37 Your cluster can now be accessed with a browser at `http://localhost:4002` or
2017/04/18 07:19:37 using `arangosh --server.endpoint tcp://localhost:4002`.

Note: In some container configuration there is not host mapping of the port exposed by the coordinator. In that case you're notified of that (and no URL is given)