Fix bad consistency level on retries

On Read/WriteTimeouts, the operation would be retried with
the same consistency level as the previous operation, but that
consistency level was erroneously being stored as a string
instead of an int, resulting in errors like
"error: cannot convert argument to integer".
Revert "Better error message for non-int consistency level"

This reverts commit c7df51c6b571cab8dea02ca763f95de96d73a564.