keys: replace mock keys client with simple mock impl for ed25519 directly
keys: replace mock keys client with simple mock impl for ed25519 directly

silasdavis/burrow,benjaminbollen/burrow,eris-ltd/eris-db,eris-ltd/eris-db,benjaminbollen/burrow,benjaminbollen/eris-db,silasdavis/burrow,benjaminbollen/eris-db,silasdavis/burrow