Add Profiler Admin API (#6463)

Two handlers are added to admin API to enable profiling and disable
profiling of a server in a standalone mode, or all nodes in the
distributed mode.

/minio/admin/profiling/start/{cpu,block,mem}:
  - Start profiling and return starting JSON results, e.g. one
    node is offline.

/minio/admin/profiling/download:
  - Stop the on-going profiling task
  - Stream a zip file which contains all profiling files that can
    be later inspected by go tool pprof

cmd/admin-rpc-server.go

@@ -52,6 +52,23 @@ func (receiver *adminRPCReceiver) ServerInfo(args *AuthArgs, reply *ServerInfoDa
 	return err
 }
 
+// StartProfilingArgs - holds the RPC argument for StartingProfiling RPC call
+type StartProfilingArgs struct {
+	AuthArgs
+	Profiler string
+}
+
+// StartProfiling - starts profiling of this server
+func (receiver *adminRPCReceiver) StartProfiling(args *StartProfilingArgs, reply *VoidReply) error {
+	return receiver.local.StartProfiling(args.Profiler)
+}
+
+// DownloadProfilingData - stops and returns profiling data of this server
+func (receiver *adminRPCReceiver) DownloadProfilingData(args *AuthArgs, reply *[]byte) (err error) {
+	*reply, err = receiver.local.DownloadProfilingData()
+	return
+}
+
 // GetConfig - returns the config.json of this server.
 func (receiver *adminRPCReceiver) GetConfig(args *AuthArgs, reply *[]byte) (err error) {
 	*reply, err = receiver.local.GetConfig()