Reduce bloat in the python RPC Response class by making better use of
superclass methods and recursion. As part of this change, add tests for
the Response class.
Test:
1. Can't login to RPC server with --rpc-login enabled, but no auth provided
2. Can access RPC server with correct login
3. Can use internal HTTP client to access RPC server with correct login
With commit 0ae5c91e50 not reverted, we fail test 3.
