Don't print terrible upstream errors

src/main.rs

@@ -345,6 +345,15 @@ pub struct Error {
     kind: ErrorKind,
 }
 
+impl Error {
+    pub(crate) fn upstream_error(&self) -> Option<&str> {
+        match self.kind {
+            ErrorKind::UploadFailed(ref msg) => Some(msg),
+            _ => None,
+        }
+    }
+}
+
 impl<T> From<T> for Error
 where
     ErrorKind: From<T>,