Return "SlowDown" to S3 clients for network related errors (#7610)

Consider errors returned by httpClient.Do() as network errors. This is because
the http clients returns different types of errors and it is hard to catch
all the error types.

cmd/api-errors.go

@@ -879,16 +879,6 @@ var errorCodes = errorCodeMap{
 		Description:    "Object name already exists as a directory.",
 		HTTPStatusCode: http.StatusConflict,
 	},
-	ErrReadQuorum: {
-		Code:           "XMinioReadQuorum",
-		Description:    "Multiple disk failures, unable to reconstruct data.",
-		HTTPStatusCode: http.StatusServiceUnavailable,
-	},
-	ErrWriteQuorum: {
-		Code:           "XMinioWriteQuorum",
-		Description:    "Multiple disks failures, unable to write data.",
-		HTTPStatusCode: http.StatusServiceUnavailable,
-	},
 	ErrInvalidObjectName: {
 		Code:           "XMinioInvalidObjectName",
 		Description:    "Object name contains unsupported characters.",
@@ -1534,7 +1524,7 @@ func toAPIErrorCode(ctx context.Context, err error) (apiErr APIErrorCode) {
 		apiErr = ErrKMSAuthFailure
 	case errOperationTimedOut, context.Canceled, context.DeadlineExceeded:
 		apiErr = ErrOperationTimedOut
-	case errNetworkConnReset:
+	case errDiskNotFound:
 		apiErr = ErrSlowDown
 	}
 
@@ -1593,9 +1583,9 @@ func toAPIErrorCode(ctx context.Context, err error) (apiErr APIErrorCode) {
 	case InvalidPart:
 		apiErr = ErrInvalidPart
 	case InsufficientWriteQuorum:
-		apiErr = ErrWriteQuorum
+		apiErr = ErrSlowDown
 	case InsufficientReadQuorum:
-		apiErr = ErrReadQuorum
+		apiErr = ErrSlowDown
 	case UnsupportedDelimiter:
 		apiErr = ErrNotImplemented
 	case InvalidMarkerPrefixCombination: