mongo-client-friendly printout for `meteor mongo --url *`

When you run `meteor mongo --url example.com` it prints out a URI. The mongo client—for some reason—doesn’t understand URIs. This commit additionally prints out a mongo-client-friendly string for connecting via the shell.

Separately, I’ve been trying a bunch to connect via the shell and I can’t connect anymore, I’m not sure if I got locked out somehow by the skybreak.member0.mongolayer.com servers. I’m pretty new to mongo, so I’m not sure if there’s a common timeout or something that people should expect.