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/admin-profiling-start.go

@@ -0,0 +1,111 @@
+/*
+ * Minio Client (C) 2018 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cmd
+
+import (
+	"strings"
+
+	"github.com/minio/cli"
+	"github.com/minio/mc/pkg/console"
+	"github.com/minio/mc/pkg/probe"
+	"github.com/minio/minio/pkg/madmin"
+)
+
+var adminProfilingStartFlags = []cli.Flag{
+	cli.StringFlag{
+		Name:  "type",
+		Usage: "Profiler type, possible values are: `cpu`, `mem`, `block`, `mutex` and `trace`",
+		Value: "mem",
+	},
+}
+
+var adminProfilingStartCmd = cli.Command{
+	Name:            "start",
+	Usage:           "Start recording profiling data",
+	Action:          mainAdminProfilingStart,
+	Before:          setGlobalsFromContext,
+	Flags:           append(adminProfilingStartFlags, globalFlags...),
+	HideHelpCommand: true,
+	CustomHelpTemplate: `NAME:
+  {{.HelpName}} - {{.Usage}}
+
+USAGE:
+  {{.HelpName}} [FLAGS] TARGET
+
+FLAGS:
+  {{range .VisibleFlags}}{{.}}
+  {{end}}
+EXAMPLES:
+    1. Start CPU profiling
+       $ {{.HelpName}} --type cpu myminio/
+
+`,
+}
+
+func checkAdminProfilingStartSyntax(ctx *cli.Context) {
+	// Check flags combinations
+	if len(ctx.Args()) != 1 {
+		cli.ShowCommandHelpAndExit(ctx, "start", 1) // last argument is exit code
+	}
+
+	profilerTypes := []madmin.ProfilerType{
+		madmin.ProfilerCPU,
+		madmin.ProfilerMEM,
+		madmin.ProfilerBlock,
+		madmin.ProfilerMutex,
+		madmin.ProfilerTrace,
+	}
+
+	// Check if the provided profiler type is known and supported
+	supportedProfiler := false
+	profilerType := strings.ToLower(ctx.String("type"))
+	for _, profiler := range profilerTypes {
+		if profilerType == string(profiler) {
+			supportedProfiler = true
+			break
+		}
+	}
+	if !supportedProfiler {
+		fatalIf(errDummy(), "Profiler type unrecognized. Possible values are: %v.", profilerTypes)
+	}
+}
+
+// mainAdminProfilingStart - the entry function of profiling command
+func mainAdminProfilingStart(ctx *cli.Context) error {
+	// Check for command syntax
+	checkAdminProfilingStartSyntax(ctx)
+
+	// Get the alias parameter from cli
+	args := ctx.Args()
+	aliasedURL := args.Get(0)
+
+	profilerType := ctx.String("type")
+
+	// Create a new Minio Admin Client
+	client, err := newAdminClient(aliasedURL)
+	if err != nil {
+		fatalIf(err.Trace(aliasedURL), "Cannot initialize admin client.")
+		return nil
+	}
+
+	// Start profiling
+	_, cmdErr := client.StartProfiling(madmin.ProfilerType(profilerType))
+	fatalIf(probe.NewError(cmdErr), "Unable to start profiling.")
+
+	console.Infoln("Profiling data successfully started.")
+	return nil
+}