Reland of PyLint fixes for tools-webrtc and webrtc/tools (patchset #1 id:1 of https://codereview.webrtc.org/2737233003/ )

Reason for revert:
Fixing errors for reland. I have tested that this does not make Chromium video quality tests fail.

Original issue's description:
> Revert of PyLint fixes for tools-webrtc and webrtc/tools (patchset #3 id:40001 of https://codereview.webrtc.org/2736233003/ )
>
> Reason for revert:
> Fails video quality tests in Chrome:  http://build.chromium.org/p/chromium.webrtc.fyi/builders/Win10%20Tester/builds/6568
> I should have looked more closer at those :(
>
> Original issue's description:
> > 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}
> > Committed: f5318e1f39
>
> TBR=oprypin@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:7303
>
> Review-Url: https://codereview.webrtc.org/2737233003
> Cr-Commit-Position: refs/heads/master@{#17142}
> Committed: 94f4d9effc

NOTRY=true
BUG=webrtc:7312

Review-Url: https://codereview.webrtc.org/2741733003
Cr-Commit-Position: refs/heads/master@{#17541}

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