Do not rely on SIGINT handler, use own handler instead

In some scenarios (e.g. our internal build server), the handler for SIGINT
is signal.SIG_IGN, i.e. the signal is ignored. In this case, the daemon will
not stop and the init script will eventually send SIGKILL, which prevents
a clean shutdown.

src/main/python/succubus/daemonize.py

@@ -138,8 +138,9 @@ def daemonize(self):
         pid = os.getpid()
         file(self.pid_file, 'w+').write("%s\n" % pid)
 
-        # Handle SIGTERM the same as SIGINT: raise a KeyboardInterrupt.
-        signal.signal(signal.SIGTERM, signal.getsignal(signal.SIGINT))
+        def handler(*args):
+            raise BaseException("SIGTERM was caught")
+        signal.signal(signal.SIGTERM, handler)
         # atexit functions are "not called when the program is killed by a
         # signal not handled by Python". But since SIGTERM is now handled, the
         # atexit functions do get called.