bug: walletdir not scoped properly for testnet

[coolaj86]

I was testing running both mainnet and testnet on the same system and found that -walletdir is being handled improperly in conjunction with -testnet.

dashd -testnet -walletdir=/home/app/.dashcore/wallets/ # ...

Expected

~/.dashcore/wallets/testnet3/

Actual

/mnt/100gb/dashcore/_data/testnet3/wallets/

How to

/home/app/.local/opt/dashcore/bin/dashd \
    -testnet \
    -usehd \
    -conf=/home/app/.dashcore/dash.conf \
    -settings=/home/app/.dashcore/settings.json \
    -walletdir=/home/app/.dashcore/wallets/ \
    -datadir=/mnt/100gb/dashcore/_data \
    -blocksdir=/mnt/100gb/dashcore/_caches

The legacy behavior causes -datadir and -blocksdir to create a testnet3 namespace under each.

/mnt/100gb/dashcore/_data/testnet3/
/mnt/100gb/dashcore/_caches/testnet3/

Although unusual and unintuitive, this is partially documented and can be worked around in a pinch with symlinks and such.

We should expect -walletdir to follow the same behavior, but it does not.

  # expected
+ /home/app/.dashcore/wallets/
  # actual
- /mnt/100gb/dashcore/_data/testnet3/wallets/