api: Add diskInfo as part of StatVol and ListVols. (#1349)

It is the bucket and volumes which needs to have this
value rather than the DiskInfo API itself. Eventually
this can be extended to show disk usage per
Buckets/Volumes whenever we have that functionality.

For now since buckets/volumes are thinly provisioned
this is the right approach.

storage-datatypes.go

@@ -1,3 +1,19 @@
+/*
+ * 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 main
 
 import (
@@ -9,6 +25,9 @@ import (
 type VolInfo struct {
 	Name    string
 	Created time.Time
+	Total   int64
+	Free    int64
+	FSType  string
 }
 
 // FileInfo - file stat information.