u_boot_pylib: Clean up pylint warnings in gitutil.py

This file has about 40 pylint warnings, but no errors.

Quite a few of these warnings have been there for a while, but most are
coming from newer versions of pylint, where people come up with new
warnings.

The f-string warning is the most common one:

   C0209: Formatting a regular string which could be an f-string

That feature was not available when the code was written, but it is
often more convenient than using % with a list of arguments.

This patches reduces the number of warnings in this file, with 7 left
remaining.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/func_test.py b/tools/buildman/func_test.py
index d779040..b45eb95 100644
--- a/tools/buildman/func_test.py
+++ b/tools/buildman/func_test.py
@@ -288,11 +288,11 @@
         """Test gitutils.Setup(), from outside the module itself"""
         command.TEST_RESULT = command.CommandResult(return_code=1)
         gitutil.setup()
-        self.assertEqual(gitutil.use_no_decorate, False)
+        self.assertEqual(gitutil.USE_NO_DECORATE, False)
 
         command.TEST_RESULT = command.CommandResult(return_code=0)
         gitutil.setup()
-        self.assertEqual(gitutil.use_no_decorate, True)
+        self.assertEqual(gitutil.USE_NO_DECORATE, True)
 
     def _HandleCommandGitLog(self, args):
         if args[-1] == '--':