flake8: Add more ignored files

* setup.py: the '__version__' variable is not defined in the script, it is loadded from youtube_dl/version.py
* devscripts/buildserver.py: Produces a lot of messages

setup.cfg

@@ -2,5 +2,5 @@
 universal = True
 
 [flake8]
-exclude = youtube_dl/extractor/__init__.py
+exclude = youtube_dl/extractor/__init__.py,devscripts/buildserver.py,setup.py
 ignore = E501