PyLint fixes for tools-webrtc and webrtc/tools

Fix a lot of errors before bringing in the new config in
https://codereview.webrtc.org/2737963003/

BUG=webrtc:7303
NOTRY=True

Review-Url: https://codereview.webrtc.org/2736233003
Cr-Commit-Position: refs/heads/master@{#17137}

tools-webrtc/gn_check_autofix.py

@@ -43,7 +43,7 @@ class TemporaryDirectory(object):
   def __enter__(self):
     return self._name
 
-  def __exit__(self, exc, value, tb):
+  def __exit__(self, exc, value, _tb):
     if self._name and not self._closed:
       shutil.rmtree(self._name)
       self._closed = True