Delete devices in various logout situations

Make sure that we delete devices whenever a user is logged out due to any of
the following situations:

 * /logout
 * /logout_all
 * change password
 * deactivate account (by the user or by an admin)
 * invalidate access token from a dynamic module

Fixes #2672.

synapse/handlers/device.py

@@ -170,13 +170,31 @@ class DeviceHandler(BaseHandler):
 
         yield self.notify_device_update(user_id, [device_id])
 
+    @defer.inlineCallbacks
+    def delete_all_devices_for_user(self, user_id, except_device_id=None):
+        """Delete all of the user's devices
+
+        Args:
+            user_id (str):
+            except_device_id (str|None): optional device id which should not
+                be deleted
+
+        Returns:
+            defer.Deferred:
+        """
+        device_map = yield self.store.get_devices_by_user(user_id)
+        device_ids = device_map.keys()
+        if except_device_id is not None:
+            device_ids = [d for d in device_ids if d != except_device_id]
+        yield self.delete_devices(user_id, device_ids)
+
     @defer.inlineCallbacks
     def delete_devices(self, user_id, device_ids):
         """ Delete several devices
 
         Args:
             user_id (str):
-            device_ids (str): The list of device IDs to delete
+            device_ids (List[str]): The list of device IDs to delete
 
         Returns:
             defer.Deferred: