Add admin profiling command (#2557)

Implement profiling command to start & download profiling data of
a standalone or all nodes of a cluster.

```
1. Start CPU profiling
   $ mc admin profiling start --type "cpu" myminio/

2. Download latest profiling data under save under profiling.zip
   $ mc admin profiling stop myminio/
```

cmd/error.go

@@ -45,6 +45,10 @@ func fatalIf(err *probe.Error, msg string, data ...interface{}) {
 	if err == nil {
 		return
 	}
+	fatal(err, msg, data...)
+}
+
+func fatal(err *probe.Error, msg string, data ...interface{}) {
 	if globalJSON {
 		errorMsg := errorMessage{
 			Message: msg,