Fix TypeError for JSONFormatter and udp2log_host

Summary:
Currently, in the case where `getMessage()` is called on a LogRecord
created by `JSONFormatter.make_record` it will fail. This is because
`JSONFormatter` treats args as a list instead of a tuple.

If there are actual args for use in the msg format string,
`getMessage()` will call:

record.msg % record.args

This will fail with something like:

'%s %s' % ['hello', 'world']
TypeError: not enough arguments for format string

Which is what happens inside the LogstashFormatter when a command fails
on a remote and the log record is propogated to Logstash. This shadows
the actual error message with:

File "/mnt/srv/deployment/scap/scap/scap/log.py", line 180, in format
    fields['message'] = fields['msg'] % fields['args']
    TypeError: not enough arguments for format string

Change-Id: I1c7360009e89aac9ab60ec5e84a4ded6af20a950

Test Plan:
On scap-vagrant:

- inside `scap/scap.cfg` set `udp2log_host: localhost`
- chown some files on the targets to create errors
- the final error should NOT be
  `TypeError: not enough arguments for format string`

Reviewers: demon, mmodell, #release-engineering-team, dduvall

Reviewed By: mmodell, #release-engineering-team, dduvall

Subscribers: jenkins

Differential Revision: https://phabricator.wikimedia.org/D83

scap/log.py

@@ -103,7 +103,7 @@ class JSONFormatter(logging.Formatter):
                 ('filename', None),
                 ('lineno', None),
                 ('msg', ''),
-                ('args', []),
+                ('args', ()),
                 ('exc_info', None),
                 ('funcName', None)]
 
@@ -120,7 +120,15 @@ class JSONFormatter(logging.Formatter):
     @staticmethod
     def make_record(data):
         fields = json.loads(data)
-        args = [fields.get(k, v) for k, v in JSONFormatter.DEFAULTS]
+        args = []
+        for k, v in JSONFormatter.DEFAULTS:
+            val = fields.get(k, v)
+
+            if k == 'args':
+                val = tuple(val)
+
+            args.append(val)
+
         record = logging.LogRecord(*args)
 
         for k in fields:

tests/scap/test_log.py

@@ -144,7 +144,7 @@ def test_make_record(self):
         self.assertIsInstance(record, logging.LogRecord)
 
         self.assertEqual(record.name, 'foo')
-        self.assertEqual(record.args, [])
+        self.assertEqual(record.args, ())
         self.assertEqual(record.filename, 'foo_file')
         self.assertEqual(record.levelno, 10)
         self.assertEqual(record.lineno, 123)