fix: Manage SSH host keys (#214)
fix: Manage SSH host keys (#214)

User's are prompted to:
- Add host keys if none are present in 'known_hosts'
- Replace stale host keys in 'known_hosts' with current keys

Host keys are added to (and removed from) both root and
the user's known_hosts files.

open-power-ref-design-toolkit/cluster-genesis,open-power-ref-design-toolkit/cluster-genesis