Change into staticmethod

It seems more appropriate to turn this function into a staticmethod

Change-Id: Ib6457216c2111f76bc873f2756feb49adcddb046
diff --git a/tempest/lib/cmd/check_uuid.py b/tempest/lib/cmd/check_uuid.py
index be3aa49..1239ac5 100755
--- a/tempest/lib/cmd/check_uuid.py
+++ b/tempest/lib/cmd/check_uuid.py
@@ -69,7 +69,8 @@
         lines[line_no - 1] = ''.join(('{%s:s}' % patch_id, lines[line_no - 1]))
         self.source_files[filename] = self._quote('\n').join(lines)
 
-    def _save_changes(self, filename, source):
+    @staticmethod
+    def _save_changes(filename, source):
         print('%s fixed' % filename)
         with open(filename, 'w') as f:
             f.write(source)