tree: fix pylint warnings

This fixes pylint warnings on our modules that are currently not part of
CI-pylint. The fixes should all be straightforward.

Signed-off-by: David Rheinsberg <david.rheinsberg@gmail.com>

devices/org.osbuild.loopback

@@ -18,11 +18,10 @@ documentation for `osbuil.util.udev.UdevInhibitor`.
 
 
 import argparse
-import errno
 import os
 import sys
 
-from typing import Dict, Optional
+from typing import Dict
 
 from osbuild import devices
 from osbuild import loop
@@ -64,6 +63,9 @@ class LoopbackService(devices.DeviceService):
     def __init__(self, args: argparse.Namespace):
         super().__init__(args)
         self.ctl = loop.LoopControl()
+        self.fd = None
+        self.lo = None
+        self.sector_size = None
 
     @staticmethod
     def setup_loop(lo: loop.Loop):