Update PS1 across all hosts to more clearly differentiate between hosts and environments

Right now our PS1s look like the following:

yorickpeterse@db1:~$

Here the username@host-part bit is green, and the path is blue. This setup is confusing because it doesn't show the environment one is in (staging vs production), the colours are the same on staging/production, and the hostname is truncated to the first segment ("db1", "worker10", etc).

To make it a bit easier to see what host you're on (whenever you need to SSH into one), we should:

• Use bold red for production, normal yellow for staging
• Show more of the hostname, either the full hostname or something like "db1.cluster" / "db1.staging", etc; either way it should include the node name and environment
• Perhaps show the path in a different color. Dark blue on the usual black background is quite hard to see, perhaps use cyan instead?