Add ServerDrivesPerfInfo() admin API (#6969)

This is part of implementation for mc admin health command. The
ServerDrivesPerfInfo() admin API returns read and write speed
information for all the drives (local and remote) in a given Minio
server deployment.

Part of minio/mc#2606

cmd/peer-rpc-server.go

@@ -238,6 +238,17 @@ func (receiver *peerRPCReceiver) LoadCredentials(args *AuthArgs, reply *VoidRepl
 	return globalConfigSys.Load(newObjectLayerFn())
 }
 
+// DrivePerfInfo - handles drive performance RPC call
+func (receiver *peerRPCReceiver) DrivePerfInfo(args *AuthArgs, reply *ServerDrivesPerfInfo) error {
+	objAPI := newObjectLayerFn()
+	if objAPI == nil {
+		return errServerNotInitialized
+	}
+
+	*reply = localEndpointsPerf(globalEndpoints)
+	return nil
+}
+
 // NewPeerRPCServer - returns new peer RPC server.
 func NewPeerRPCServer() (*xrpc.Server, error) {
 	rpcServer := xrpc.NewServer()