wallettool: Optionally use BERKELEY_RO as format when dumping BDB wallets

In order to ease the transition to not having BDB, make the dump tool
use DatabaseFormmat::BERKELEY_RO when -withinternalbdb is set.

test/functional/test_runner.py

@@ -192,6 +192,7 @@ BASE_SCRIPTS = [
     'mempool_resurrect.py',
     'wallet_txn_doublespend.py --mineblock',
     'tool_wallet.py --legacy-wallet',
+    'tool_wallet.py --legacy-wallet --bdbro',
     'tool_wallet.py --descriptors',
     'tool_signet_miner.py --legacy-wallet',
     'tool_signet_miner.py --descriptors',