Bug 434480

This is an API request that could solve an issue in [Keyring](https://github.com/jaraco/keyring), the most widely used python keyring library, and perhaps other similar libraries/clients.

Consider the following scenario, as described in this [bug report](https://github.com/jaraco/keyring/issues/496):
- Gnome Shell user, KWallet was pulled as dependency of some installed KDE utility but never actually used.
- Keyring, when asked for a (non-existing) password, looks for it in every registered backend, including KWallet.
- Some DBus calls are made to _query_ if a password exists in KWallet:
    - opening `org.kde.kwalletd5/modules/kwalletd5.networkWallet()` DBus interface
    - `.hasEntry()` to check if password exists (in this example, it doesn't)
    - if hasEntry succeeds, `.readPassword()` to finally get the data.

Since no Wallet exists, KWalled pops up its Wallet Creation GUI! A very undesirable side-effect when merely querying for password existence. After all, if there is no Wallet then `.hasEntry()` could (should?) have short-circuited to say **no**.

Either approach could solve that problem:
- `.networkWallet()`/`.hasEntry()` could _not_ trigger Wallet creation, either by default (preferable) or by a `create=False` flag parameter, that could default to `True` to preserve backward-compatibility with current behavior.
- A method/interface that allow clients to probe if Wallet infrastructure exists prior to issuing `.networkWallet()`/`.hasEntry()`. Is there any such method already?

Relevant (python) code that trigger the undesirable wallet creation GUI, if that helps:

https://github.com/jaraco/keyring/blob/02f341401df8063e0a962ddc4fe73c06e59068a3/keyring/backends/kwallet.py#L89-L116
```python
    def connected(self, service):
        if self.handle >= 0:
            if self.iface.isOpen(self.handle):
                return True


        bus = dbus.SessionBus(mainloop=DBusGMainLoop())
        wId = 0
        try:
            remote_obj = bus.get_object(self.bus_name, self.object_path)
            self.iface = dbus.Interface(remote_obj, 'org.kde.KWallet')
            self.handle = self.iface.open(self.iface.networkWallet(), wId, self.appid)
        except dbus.DBusException as e:
            raise InitError('Failed to open keyring: %s.' % e)


        if self.handle < 0:
            return False
        self._migrate(service)
        return True


    def get_password(self, service, username):
        """Get password of the username for the service"""
        if not self.connected(service):
            # the user pressed "cancel" when prompted to unlock their keyring.
            raise KeyringLocked("Failed to unlock the keyring!")
        if not self.iface.hasEntry(self.handle, service, username, self.appid):
            return None
        password = self.iface.readPassword(self.handle, service, username, self.appid)
        return str(password)
```