Code review comment for ~ddstreet/software-properties:simple_http_unix_connection

I believe I tested this successfully in 20.04, with minor backporting. The following changes are necessary on top of ecf462b:

1. `sock.sock = sock` should be `self.sock = sock`
2. A reference to `self.LIVEPATCH_RUNNING_FILE` should be to `LIVEPATCH_RUNNING_FILE` instead