Fix variable shadowing in test/wallet_tests.cpp
Fix variable shadowing in test/wallet_tests.cpp

wallet/test/wallet_tests.cpp:225:18: warning: declaration shadows a local variable [-Wshadow]
        for (int i = 0; i < 20; i++)
                 ^
wallet/test/wallet_tests.cpp:304:22: warning: declaration shadows a local variable [-Wshadow]
            for (int i = 0; i < RANDOM_REPEATS; i++)
                     ^
wallet/test/wallet_tests.cpp:321:22: warning: declaration shadows a local variable [-Wshadow]
            for (int i = 0; i < RANDOM_REPEATS; i++)
                     ^
wallet/test/wallet_tests.cpp:81:14: note: previous declaration is here
    for (int i = 0; i < RUN_TESTS; i++)
             ^

Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,Justaphf/BitcoinUnlimited,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,Justaphf/BitcoinUnlimited,Justaphf/BitcoinUnlimited,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited