fs/xl: Combine input checks into re-usable functions. (#3383)

Repeated code around both object layers are moved
and combined into simple re-usable functions.

cmd/fs-v1-multipart-common_test.go

@@ -23,39 +23,6 @@ import (
 	"time"
 )
 
-// TestFSIsBucketExist - complete test of isBucketExist
-func TestFSIsBucketExist(t *testing.T) {
-	// Prepare for testing
-	disk := filepath.Join(os.TempDir(), "minio-"+nextSuffix())
-	defer removeAll(disk)
-
-	obj := initFSObjects(disk, t)
-	fs := obj.(fsObjects)
-	bucketName := "bucket"
-
-	if err := obj.MakeBucket(bucketName); err != nil {
-		t.Fatal("Cannot create bucket, err: ", err)
-	}
-
-	// Test with a valid bucket
-	if found := fs.isBucketExist(bucketName); !found {
-		t.Fatal("isBucketExist should true")
-	}
-
-	// Test with a inexistant bucket
-	if found := fs.isBucketExist("foo"); found {
-		t.Fatal("isBucketExist should false")
-	}
-
-	// Using a faulty disk
-	fsStorage := fs.storage.(*retryStorage)
-	naughty := newNaughtyDisk(fsStorage, nil, errFaultyDisk)
-	fs.storage = naughty
-	if found := fs.isBucketExist(bucketName); found {
-		t.Fatal("isBucketExist should return false because it is wired to a corrupted disk")
-	}
-}
-
 // TestFSIsUploadExists - complete test with valid and invalid cases
 func TestFSIsUploadExists(t *testing.T) {
 	// Prepare for testing