Fix a deprecation warning about threading.Thread

Fix the following deprecation warning.

* DeprecationWarning: setDaemon() is deprecated,
  set the daemon attribute instead

Change-Id: I7af41eddf597e1ac78e8835a5af2e029d65a302a
Closes-Bug: 1987191
Signed-off-by: Takashi Natsume <[email protected]>

Author: takanattie

glance/api/v2/cached_images.py

@@ -257,7 +257,7 @@ def __init__(self, *args, **kwargs):
         # NOTE(abhishekk): Setting daemon to True because if `atexit` event
         # handler is not called due to some reason the main process will
         # not hang for the thread which will never exit.
-        self.setDaemon(True)
+        self.daemon = True
 
     def submit(self, job):
         self.q.put(job)