Add notifications by webhook.

Add a new config entry moving to version 13.
```
		"webhook": {
			"1": {
				"enable": true,
				"address": "http://requestb.in/1i9al7m1"
			}
		}
```

cmd/config-v13_test.go

@@ -0,0 +1,112 @@
+/*
+ * Minio Cloud Storage, (C) 2016 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 (
+	"reflect"
+	"testing"
+)
+
+func TestServerConfig(t *testing.T) {
+	rootPath, err := newTestConfig("us-east-1")
+	if err != nil {
+		t.Fatalf("Init Test config failed")
+	}
+	// remove the root directory after the test ends.
+	defer removeAll(rootPath)
+
+	if serverConfig.GetRegion() != "us-east-1" {
+		t.Errorf("Expecting region `us-east-1` found %s", serverConfig.GetRegion())
+	}
+
+	// Set new region and verify.
+	serverConfig.SetRegion("us-west-1")
+	if serverConfig.GetRegion() != "us-west-1" {
+		t.Errorf("Expecting region `us-west-1` found %s", serverConfig.GetRegion())
+	}
+
+	// Set new amqp notification id.
+	serverConfig.SetAMQPNotifyByID("2", amqpNotify{})
+	savedNotifyCfg1 := serverConfig.GetAMQPNotifyByID("2")
+	if !reflect.DeepEqual(savedNotifyCfg1, amqpNotify{}) {
+		t.Errorf("Expecting AMQP config %#v found %#v", amqpNotify{}, savedNotifyCfg1)
+	}
+
+	// Set new elastic search notification id.
+	serverConfig.SetElasticSearchNotifyByID("2", elasticSearchNotify{})
+	savedNotifyCfg2 := serverConfig.GetElasticSearchNotifyByID("2")
+	if !reflect.DeepEqual(savedNotifyCfg2, elasticSearchNotify{}) {
+		t.Errorf("Expecting Elasticsearch config %#v found %#v", elasticSearchNotify{}, savedNotifyCfg2)
+	}
+
+	// Set new redis notification id.
+	serverConfig.SetRedisNotifyByID("2", redisNotify{})
+	savedNotifyCfg3 := serverConfig.GetRedisNotifyByID("2")
+	if !reflect.DeepEqual(savedNotifyCfg3, redisNotify{}) {
+		t.Errorf("Expecting Redis config %#v found %#v", redisNotify{}, savedNotifyCfg3)
+	}
+
+	// Set new kafka notification id.
+	serverConfig.SetKafkaNotifyByID("2", kafkaNotify{})
+	savedNotifyCfg4 := serverConfig.GetKafkaNotifyByID("2")
+	if !reflect.DeepEqual(savedNotifyCfg4, kafkaNotify{}) {
+		t.Errorf("Expecting Kafka config %#v found %#v", kafkaNotify{}, savedNotifyCfg4)
+	}
+
+	// Set new Webhook notification id.
+	serverConfig.SetWebhookNotifyByID("2", webhookNotify{})
+	savedNotifyCfg5 := serverConfig.GetWebhookNotifyByID("2")
+	if !reflect.DeepEqual(savedNotifyCfg5, webhookNotify{}) {
+		t.Errorf("Expecting Webhook config %#v found %#v", webhookNotify{}, savedNotifyCfg3)
+	}
+
+	// Set new console logger.
+	serverConfig.SetConsoleLogger(consoleLogger{
+		Enable: true,
+	})
+	consoleCfg := serverConfig.GetConsoleLogger()
+	if !reflect.DeepEqual(consoleCfg, consoleLogger{Enable: true}) {
+		t.Errorf("Expecting console logger config %#v found %#v", consoleLogger{Enable: true}, consoleCfg)
+	}
+
+	// Set new file logger.
+	serverConfig.SetFileLogger(fileLogger{
+		Enable: true,
+	})
+	fileCfg := serverConfig.GetFileLogger()
+	if !reflect.DeepEqual(fileCfg, fileLogger{Enable: true}) {
+		t.Errorf("Expecting file logger config %#v found %#v", fileLogger{Enable: true}, consoleCfg)
+	}
+
+	// Match version.
+	if serverConfig.GetVersion() != globalMinioConfigVersion {
+		t.Errorf("Expecting version %s found %s", serverConfig.GetVersion(), globalMinioConfigVersion)
+	}
+
+	// Attempt to save.
+	if err := serverConfig.Save(); err != nil {
+		t.Fatalf("Unable to save updated config file %s", err)
+	}
+
+	// Do this only once here.
+	setGlobalConfigPath(rootPath)
+
+	// Initialize server config.
+	if _, err := initConfig(); err != nil {
+		t.Fatalf("Unable to initialize from updated config file %s", err)
+	}
+}