PEP8 cleanup for node/market.py through node/openbazaar.py

Minor PEP8 clean up commit 2 of 3.
Please don't use backslashes unless necessary. Here's an alternative:
```python
result_tcp_p2p_mapping = self.upnp_mapper.add_port_mapping(
    p2p_port, p2p_port
)
```
Ditto with the UDP mapping.