Bring back auto ssh key generation

[aaronsteers]

These ssh key files used to be generated automatically but that led to some weird cases where subsequent executions would fail due to the files already existing.

• Ideally would be nice to have a smoother onramp, since many people don't know how to create SSH keypairs and it is a cumbersome (but necessary) part of the process.

Originally posted by @aaronsteers in https://github.com/slalom-ggp/dataops-infra/diffs