*: move logging to embed, disable grpc server log by default

[gyuho]

Remove grpc logs when --debug=false:

WARNING: 2017/11/02 11:35:51 grpc: addrConn.resetTransport failed to create client transport: connection error: desc = "transport: Error while dialing dial tcp: operation was canceled"; Reconnecting to {localhost:2379 <nil>}
WARNING: 2017/11/02 11:35:51 grpc: addrConn.resetTransport failed to create client transport: connection error: desc = "transport: Error while dialing dial tcp: operation was canceled"; Reconnecting to {localhost:2379 <nil>}
INFO: 2017/11/02 11:35:51 get error from resetTransport grpc: the connection is closing, transportMonitor returning

[xiang90]

lgtm

[fanminshi]

lgtm