Implement list, clear locks REST API w/ pkg/madmin support (#3491)

* Filter lock info based on bucket, prefix and time since lock was held
* Implement list and clear locks REST API
* madmin: Add list and clear locks API
* locks: Clear locks matching bucket, prefix, relTime.
* Gather lock information across nodes for both list and clear locks admin REST API.
* docs: Add lock API to management APIs

cmd/api-errors.go

@@ -110,6 +110,7 @@ const (
 	ErrInvalidQuerySignatureAlgo
 	ErrInvalidQueryParams
 	ErrBucketAlreadyOwnedByYou
+	ErrInvalidDuration
 	// Add new error codes here.
 
 	// Bucket notification related errors.
@@ -477,6 +478,11 @@ var errorCodeResponse = map[APIErrorCode]APIError{
 		Description:    "Your previous request to create the named bucket succeeded and you already own it.",
 		HTTPStatusCode: http.StatusConflict,
 	},
+	ErrInvalidDuration: {
+		Code:           "InvalidDuration",
+		Description:    "Relative duration provided in the request is invalid.",
+		HTTPStatusCode: http.StatusBadRequest,
+	},
 
 	/// Bucket notification related errors.
 	ErrEventNotification: {