pushimage: fix tobesigned state file

We write out some debugging states to the tobesigned files.  The python
rewrite added a bug where newlines were omitted between the entries.
This isn't a big problem as the content isn't used directly (it's meant
for humans trying to debug stuff), but let's fix it anyway.  For the
humans.

BUG=None
TEST=`./scripts/pushimage_unittest.py` passes

Change-Id: I7950e66ee08b811a6e06c41e94d9748f579b3f96
Reviewed-on: https://chromium-review.googlesource.com/184810
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/pushimage_unittest.py b/scripts/pushimage_unittest.py
index aeb91f5..3cd9849 100755
--- a/scripts/pushimage_unittest.py
+++ b/scripts/pushimage_unittest.py
@@ -154,9 +154,10 @@
     pushimage.MarkImageToBeSigned(self.ctx, '', '', 50)
     # We assume the first call is the one we care about.
     self.assertTrue(m.called)
-    content = '\n'.join(m.call_args_list[0][0][1])
+    content = m.call_args_list[0][0][1]
     self.assertIn('USER=', content)
     self.assertIn('HOSTNAME=', content)
+    self.assertIn('\n', content)
 
   def testTbsUpload(self):
     """Make sure we actually try to upload the file"""