Make responses work with bitcoin-cli

[Sergi Delgado]

Currently the mock responses can be properly parsed by AuthServiceProxy (like the python-bitcoinrpc package). However, bitcoin-cli cannot parse the replies from the server.

Fix the format so it work for both.

e.g:

> bitcoin-cli getblock fa455bfb4caafd88881e7367e78bb116ea1bffb959fecd0d10d80a9c2a27dd40

error: couldn't parse reply from server