journal: fix repr of JournalHandler to match python3.6

We get <systemd.journal.JournalHandler object at ...> in older versions,
and <JournalHandler (NOTSET)> in since Python 3.6.
python/cpython@c075201

Author: keszybz

systemd/journal.py

@@ -542,7 +542,7 @@ class JournalHandler(_logging.Handler):
     program:
 
     >>> JournalHandler(SYSLOG_IDENTIFIER='my-cool-app')
-    <systemd.journal.JournalHandler object at ...>
+    <...JournalHandler ...>
 
     The following journal fields will be sent: `MESSAGE`, `PRIORITY`,
     `THREAD_NAME`, `CODE_FILE`, `CODE_LINE`, `CODE_FUNC`, `LOGGER` (name as