[qa] Add shrinkdebugfile=0 to regtest bitcoin.conf
[qa] Add shrinkdebugfile=0 to regtest bitcoin.conf

This helps avoid accidentally truncating the debug.log while manually
debugging.

DigitalPandacoin/pandacoin,peercoin/peercoin,peercoin/peercoin,DigitalPandacoin/pandacoin,peercoin/peercoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,peercoin/peercoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,peercoin/peercoin,peercoin/peercoin