Handle rest exceptions without http_body -timeout exeptions-  / #issue 10

*This PR intentes to identify the issue reported on #10 and if needed implement the required code fixes.*

**After some investigation it resulted to be a problem with Rest timeout exceptions which came without http_body.**

- [x]  Added spec to replicate problem and validate fix
- [x]  Added logic to prevent using the http_body attribute to form the `Openpayexception` when nil