test: Rename wallet.dat to wallet_test.dat
test: Rename wallet.dat to wallet_test.dat

Indicate that the file name is not hardcoded, and a little bit of safety
so that it never nukes the main wallet.

Suggestion by Marco Falke.

BTCfork/hardfork_prototype_1_mvf-bu,Bitcoin-com/BUcash,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,Bitcoin-com/BUcash,BitcoinUnlimited/BitcoinUnlimited,Justaphf/BitcoinUnlimited,Justaphf/BitcoinUnlimited,marcusdiaz/BitcoinUnlimited,BTCfork/hardfork_prototype_1_mvf-bu,marcusdiaz/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,BTCfork/hardfork_prototype_1_mvf-bu,Bitcoin-com/BUcash,Justaphf/BitcoinUnlimited,marcusdiaz/BitcoinUnlimited,cddjr/BitcoinUnlimited,krzysztofwos/BitcoinUnlimited,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,marcusdiaz/BitcoinUnlimited,Justaphf/BitcoinUnlimited,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,marcusdiaz/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,krzysztofwos/BitcoinUnlimited,Bitcoin-com/BUcash,cddjr/BitcoinUnlimited,cddjr/BitcoinUnlimited,cddjr/BitcoinUnlimited,BTCfork/hardfork_prototype_1_mvf-bu,marcusdiaz/BitcoinUnlimited,krzysztofwos/BitcoinUnlimited,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,krzysztofwos/BitcoinUnlimited,Bitcoin-com/BUcash,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,BTCfork/hardfork_prototype_1_mvf-bu,Bitcoin-com/BUcash,cddjr/BitcoinUnlimited,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,krzysztofwos/BitcoinUnlimited,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,BitcoinUnlimited/BitcoinUnlimited,BTCfork/hardfork_prototype_1_mvf-bu,krzysztofwos/BitcoinUnlimited,cddjr/BitcoinUnlimited