* Refactoring openssh_keypair for multiple backends
* Fixing cryptography backend validations
* Simplifying conditionals and excess variable assignments
* Fixing docs and adding cleanup for integration tests
* Fixing docs and public key validation bugs in crypto backend
* Enhancing cryptogagraphy utils to raise OpenSSHErrors when file not found
* Adding missed copyright and cleanup for idempotency test keys
* Fixing doc style
* Readding crypto/openssh for backwards compatibility
* Adding changelog fragment and final simplifications of conditional statements
* Applied initial review suggestions
Ajpantuso