Show master address and login command after launch

[nchammas]

This is a belated response to a suggestion (I believe originally by @engrean) to show the master address immediately after launch to make it easy for people to find the Spark UI without having to run a separate describe. I originally resisted but now I think it would be useful.

I also added a brief note showing how to login to the cluster after seeing several people manually look up the master address and login using plain SSH. Did anyone else do this when they first started using Flintrock?

New output:

$ flintrock launch nick --no-install-spark
Launching 2 instances...
[54.89.148.191] SSH online.
[54.89.148.191] Configuring ephemeral storage...
[54.89.148.191] Installing Java 1.8...
[52.23.251.87] SSH online.
[52.23.251.87] Configuring ephemeral storage...
[52.23.251.87] Installing Java 1.8...
launch finished in 0:02:49.
Cluster master: ec2-52-23-251-87.compute-1.amazonaws.com
Login with: flintrock login nick

It's not the cleanest output honestly, but it's practical and will do fine until we get around to #27.

[BenFradet]

@nchammas I used plain SSH and wasn't aware of a login command :+1:

[nchammas]

@BenFradet - Oh, interesting!

How did you look up the master address in order to SSH? Did you use describe, or the AWS web console, or something else?

[BenFradet]

Both alternatively depending on whether I had the console open.

The worst part is I've seen much of the codebase before, I guess I just skipped right through that one :(

[nchammas]

😆 There are probably many other people doing the same!

Alright, hopefully with this little change we can eliminate that problem. 👍