Add loadwallet and createwallet RPC load_on_startup options

This maintains a persistent list of wallets stored in settings that will
automatically be loaded on startup. Being able to load a wallet automatically
on startup will be more useful in the GUI when the option to create wallets is
added in #15006, but it's reasonable to expose this feature by RPC as well.

test/functional/wallet_startup.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python3
+# Copyright (c) 2017-2019 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Test wallet load on startup.
+
+Verify that a bitcoind node can maintain list of wallets loading on startup
+"""
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import (
+    assert_equal,
+)
+
+
+class WalletStartupTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.setup_clean_chain = True
+        self.num_nodes = 1
+        self.supports_cli = True
+
+    def skip_test_if_missing_module(self):
+        self.skip_if_no_wallet()
+
+    def setup_nodes(self):
+        self.add_nodes(self.num_nodes)
+        self.start_nodes()
+
+    def run_test(self):
+        self.nodes[0].createwallet(wallet_name='w0', load_on_startup=True)
+        self.nodes[0].createwallet(wallet_name='w1', load_on_startup=False)
+        self.nodes[0].createwallet(wallet_name='w2', load_on_startup=True)
+        self.nodes[0].createwallet(wallet_name='w3', load_on_startup=False)
+        self.nodes[0].createwallet(wallet_name='w4', load_on_startup=False)
+        self.nodes[0].unloadwallet(wallet_name='w0', load_on_startup=False)
+        self.nodes[0].unloadwallet(wallet_name='w4', load_on_startup=False)
+        self.nodes[0].loadwallet(filename='w4', load_on_startup=True)
+        assert_equal(set(self.nodes[0].listwallets()), set(('', 'w1', 'w2', 'w3', 'w4')))
+        self.restart_node(0)
+        assert_equal(set(self.nodes[0].listwallets()), set(('', 'w2', 'w4')))
+        self.nodes[0].unloadwallet(wallet_name='', load_on_startup=False)
+        self.nodes[0].unloadwallet(wallet_name='w4', load_on_startup=False)
+        self.nodes[0].loadwallet(filename='w3', load_on_startup=True)
+        self.nodes[0].loadwallet(filename='')
+        self.restart_node(0)
+        assert_equal(set(self.nodes[0].listwallets()), set(('w2', 'w3')))
+
+if __name__ == '__main__':
+    WalletStartupTest().main()