[3095] Rename log message ID

The UNHANDLED_EXCEPTION is renamed to PYTHON_UNHANDLED_EXCEPTION,
because only python code produces this one.

src/lib/python/isc/util/traceback_handler.py

@@ -35,5 +35,5 @@ def traceback_handler(main):
         fd, name = tempfile.mkstemp(text=True)
         with os.fdopen(fd, 'w') as handle:
             traceback.print_exc(None, handle)
-        logger.fatal(UNHANDLED_EXCEPTION, type(e).__name__, e, name)
+        logger.fatal(PYTHON_UNHANDLED_EXCEPTION, type(e).__name__, e, name)
         sys.exit(1)

src/lib/python/isc/util/util_messages.mes

@@ -15,7 +15,7 @@
 # No namespace declaration - these constants go in the global namespace
 # of the isc.util.util_messages python module.
 
-% UNHANDLED_EXCEPTION program terminated with exception %1: %2. More info in %3
+% PYTHON_UNHANDLED_EXCEPTION program terminated with exception %1: %2. More info in %3
 A program encountered an unexpected situation and terminated because it
 didn't know how to handle it. The exact problem is logged in the
 message. This might be caused by a bug in the program, a broken