test, refactor: add default_wallet_name and wallet_data_filename variables

No changes in behavior

test/functional/interface_bitcoin_cli.py

@@ -95,7 +95,7 @@ class TestBitcoinCli(BitcoinTestFramework):
             assert_equal(self.nodes[0].cli.getwalletinfo(), wallet_info)
 
             # Setup to test -getinfo, -generate, and -rpcwallet= with multiple wallets.
-            wallets = ['', 'Encrypted', 'secret']
+            wallets = [self.default_wallet_name, 'Encrypted', 'secret']
             amounts = [BALANCE + Decimal('9.999928'), Decimal(9), Decimal(31)]
             self.nodes[0].createwallet(wallet_name=wallets[1])
             self.nodes[0].createwallet(wallet_name=wallets[2])