Refactor bucket delete and bucket policy (#5580)

This commit adds the bucket delete and bucket policy functionalities
to the browser.

Part of rewriting the browser code to follow best practices and
guidelines of React (issues #5409 and #5410)

The backend code has been modified by @krishnasrinivas to prevent
issue #4498 from occuring. The relevant changes have been made to the
code according to the latest commit and the unit tests in the backend.
This commit also addresses issue #5449.

cmd/generic-handlers.go

@@ -280,7 +280,7 @@ func (h minioReservedBucketHandler) ServeHTTP(w http.ResponseWriter, r *http.Req
 	default:
 		// For all other requests reject access to reserved
 		// buckets
-		bucketName, _ := urlPath2BucketObjectName(r.URL)
+		bucketName, _ := urlPath2BucketObjectName(r.URL.Path)
 		if isMinioReservedBucket(bucketName) || isMinioMetaBucket(bucketName) {
 			writeErrorResponse(w, ErrAllAccessDisabled, r.URL)
 			return
@@ -439,7 +439,7 @@ var notimplementedObjectResourceNames = map[string]bool{
 
 // Resource handler ServeHTTP() wrapper
 func (h resourceHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
-	bucketName, objectName := urlPath2BucketObjectName(r.URL)
+	bucketName, objectName := urlPath2BucketObjectName(r.URL.Path)
 
 	// If bucketName is present and not objectName check for bucket level resource queries.
 	if bucketName != "" && objectName == "" {