On my Linux Mint 19.1:
```bash
$ umask
0022
```

After the first run of `bitcoin-qt -sysperm=false` the `0700` permissions are expected for both the datadir (`~/.bitcoin`) and the walletdir (`~/.bitcoin/wallets`).

Actually, the directories are created with such access permissions:
```bash
$ stat ~/.bitcoin | grep Uid
Access: (0755/drwxr-xr-x)  Uid: ( 1000/ hebasto)   Gid: ( 1000/ hebasto)
$ stat ~/.bitcoin/wallets | grep Uid
Access: (0755/drwxr-xr-x)  Uid: ( 1000/ hebasto)   Gid: ( 1000/ hebasto)
```

Refs:
- #4286
- #13371
- #13389

NOTE: reading through the initial PR #4286 makes me think it was controversial. Is it a better and simpler way to just get rid of `-sysperm` option? I believe a user who needs this option can easily run `chown` command.
{
#if HAVE_SYSTEM
    ShutdownNotify(*node.args);
#endif
    InterruptHTTPServer();
    InterruptHTTPRPC();
    InterruptRPC();
    InterruptREST();
    InterruptTorControl();
    InterruptMapPort();
    if (node.connman)
        node.connman->Interrupt();
    if (g_txindex) {
        g_txindex->Interrupt();
    }
    ForEachBlockFilterIndex([](BlockFilterIndex& index) { index.Interrupt(); });
    if (g_coin_stats_index) {
        g_coin_stats_index->Interrupt();
    }
}
void Shutdown(NodeContext& node)