Default facility to None in OSJournalHandler class

Use a default value of None for facility in OSJournalHandler
class, as is done in the OSSysLogHandler class.

Neutron started failing with a:

 E1120: No value for argument 'facility' in constructor call

With a recent release of oslo.log.

Change-Id: I5269b82d219fd2377535120d9d266238d50431b3
Related-Bug: #1871840
(cherry picked from commit 184235c265)

oslo_log/handlers.py

@@ -82,7 +82,7 @@ class OSJournalHandler(logging.Handler):
         'request_id',
     )
 
-    def __init__(self, facility):
+    def __init__(self, facility=None):
         if not journal:
             raise RuntimeError("Systemd bindings do not exist")
 

oslo_log/tests/unit/test_log.py

@@ -29,6 +29,10 @@ try:
     import syslog
 except ImportError:
     syslog = None
+try:
+    from systemd import journal
+except ImportError:
+    journal = None
 import tempfile
 import time
 from unittest import mock
@@ -390,6 +394,15 @@ class OSJournalHandlerTestCase(BaseTestCase):
         self.addCleanup(self.journal.stop)
         log.setup(self.CONF, 'testing')
 
+    @testtools.skipUnless(journal, "systemd journal binding is not available")
+    def test_handler(self):
+        handler = handlers.OSJournalHandler()
+        handler.emit(
+            logging.LogRecord("foo", logging.INFO,
+                              "path", 123, "hey!",
+                              None, None))
+        self.assertTrue(self.journal.send.called)
+
     def test_emit(self):
         logger = log.getLogger('nova-test.foo')
         local_context = _fake_new_context()