Fix the emulator with autotools

Summary:
Accessing an undefined array key inside an if statement doesn't fail
the if but raises an exception. This is causing the python script
relying on this to check for the EMULATOR entry in the config file to
fail. This diff adds a dummy EMULATOR entry in the autotools config.ini
template to avoid this issue.

Test Plan:

make check

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5883