Create base Daemon class and refactor Undertaker to inherit from base…

… class; rucio#6478

Initial commit where base class Daemon is created. As an initial test,
Undertaker inherits from Daemon. If tests pass, other daemons
can also be refactored to inherit from Daemon.

bin/rucio-undertaker

@@ -21,7 +21,7 @@ Undertaker is a daemon to manage expired did.
 import argparse
 import signal
 
-from rucio.daemons.undertaker.undertaker import run, stop
+from rucio.daemons.undertaker.undertaker import Undertaker
 
 
 def get_parser():
@@ -66,12 +66,11 @@ Check if the DID exists::
 
 
 if __name__ == "__main__":
-
-    signal.signal(signal.SIGTERM, stop)
     parser = get_parser()
     args = parser.parse_args()
+    undertaker = Undertaker(total_workers=args.total_workers, chunk_size=args.chunk_size, once=args.run_once, sleep_time=args.sleep_time)
+    signal.signal(signal.SIGTERM, undertaker.stop)
     try:
-        run(total_workers=args.total_workers, chunk_size=args.chunk_size, once=args.run_once,
-            sleep_time=args.sleep_time)
+        undertaker.run()
     except KeyboardInterrupt:
-        stop()
+        undertaker.stop()