explicit flush stdout/stderr before exit, because of possible buffered output in python (echo or grep fail2ban-client --version can sometimes returns nothing)

fail2ban/client/fail2bancmdline.py

@@ -270,6 +270,10 @@ class Fail2banCmdLine():
 	@staticmethod
 	def exit(code=0):
 		logSys.debug("Exit with code %s", code)
+		# because of possible buffered output in python, we should flush it before exit:
+		sys.stdout.flush()
+		sys.stderr.flush()
+		# exit
 		Fail2banCmdLine._exit(code)