Move to another RPC system

[draftcode]

Currently, RRRSpec uses Redis as a RPC system and as a temporary data store. It needs some persistence actions from Redis to MySQL, and it increases unnecessary complexities. Move to another RPC system like MsgPack-RPC or ProtocolBuffers to let the workers and the masters communicate in a simpler way.

• Create Notification API
• Create Master API
• Create Worker API
• Make {worker,master,slave} runners to use API
• Start-up code of API Server
• Finish all worker_logs created by disconnected workers