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: https://chromium.googlesource.com/external/webrtc/+/f5318e1f391859c82aaa47b297429e50f41f6b3c

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}
diff --git a/webrtc/tools/barcode_tools/helper_functions.py b/webrtc/tools/barcode_tools/helper_functions.py
index e27322f..fb9854f8 100644
--- a/webrtc/tools/barcode_tools/helper_functions.py
+++ b/webrtc/tools/barcode_tools/helper_functions.py
@@ -20,7 +20,7 @@
   pass
 
 
-def ZeroPad(number, padding=_DEFAULT_PADDING):
+def zero_pad(number, padding=_DEFAULT_PADDING):
   """Converts an int into a zero padded string.
 
   Args:
@@ -35,7 +35,7 @@
   return str(number).zfill(padding)
 
 
-def RunShellCommand(cmd_list, fail_msg=None):
+def run_shell_command(cmd_list, fail_msg=None):
   """Executes a command.
 
   Args:
@@ -60,8 +60,8 @@
   return output.strip()
 
 
-def PerformActionOnAllFiles(directory, file_pattern, file_extension,
-                            start_number, action, **kwargs):
+def perform_action_on_all_files(directory, file_pattern, file_extension,
+                                start_number, action, **kwargs):
   """Function that performs a given action on all files matching a pattern.
 
   It is assumed that the files are named file_patternxxxx.file_extension, where
@@ -86,7 +86,7 @@
   process_pool = multiprocessing.Pool(processes=multiprocessing.cpu_count())
   results = []
   while True:
-    zero_padded_file_number = ZeroPad(file_number)
+    zero_padded_file_number = zero_pad(file_number)
     file_name = file_prefix + zero_padded_file_number + '.' + file_extension
     if not os.path.isfile(file_name):
       break