Audit validator key generation; ensure compatibility w/ rippled Ed25519 implementation @ripple-keypairs

[khancode]

We want to verify that we are generating correct validator keys.

Original issue: https://github.com/ripple/ripple-keypairs/issues/85

[JST5000]

@intelliot Does this still need to be done? (At this point it seems that if there was an issue it would've been reported)