Add RPC test showing correct handling of JS txns from blockchain

For unencrypted wallets, the wallet correctly tracks JoinSplits made for their
zkey in a different wallet.

qa/pull-tester/rpc-tests.sh

@@ -12,6 +12,7 @@ export BITCOIND=${REAL_BITCOIND}
 
 testScripts=(
     'wallet.py'
+    'wallet_nullifiers.py'
     'listtransactions.py'
     'mempool_resurrect_test.py'
     'txn_doublespend.py'