Migrate all backend at .minio.sys/config to encrypted backend (#8474)

- Supports migrating only when the credential ENVs are set,
  so any FS mode deployments which do not have ENVs set will
  continue to remain as is.
- Credential ENVs can be rotated using MINIO_ACCESS_KEY_OLD
  and MINIO_SECRET_KEY_OLD envs, in such scenarios it allowed
  to rotate the encrypted content to a new admin key.

cmd/test-utils_test.go

@@ -523,13 +523,13 @@ func newTestConfig(bucketLocation string, obj ObjectLayer) (err error) {
 		return err
 	}
 
-	logger.Disable = true
-
 	globalActiveCred = auth.Credentials{
 		AccessKey: auth.DefaultAccessKey,
 		SecretKey: auth.DefaultSecretKey,
 	}
 
+	globalConfigEncrypted = true
+
 	// Set a default region.
 	config.SetRegion(globalServerConfig, bucketLocation)