Use pylint 2.7 for depot_tools

This includes a few fixes for specific errors, and disables several new
warnings introduced in this version, in order to allow for an incremental migration.

Bug:1262286
Change-Id: I4b8f8fc521386419a3121bbb07edc8ac83170a94
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3413679
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>
diff --git a/fetch.py b/fetch.py
index c4b605c..74b2298 100755
--- a/fetch.py
+++ b/fetch.py
@@ -56,7 +56,6 @@
 
   def exists(self):
     """Check does this checkout already exist on desired location"""
-    pass
 
   def init(self):
     pass
@@ -67,18 +66,18 @@
       return ''
     if return_stdout:
       return subprocess.check_output(cmd, **kwargs).decode()
-    else:
-      try:
-        subprocess.check_call(cmd, **kwargs)
-      except subprocess.CalledProcessError as e:
-        # If the subprocess failed, it likely emitted its own distress message
-        # already - don't scroll that message off the screen with a stack trace
-        # from this program as well. Emit a terse message and bail out here;
-        # otherwise a later step will try doing more work and may hide the
-        # subprocess message.
-        print('Subprocess failed with return code %d.' % e.returncode)
-        sys.exit(e.returncode)
-      return ''
+
+    try:
+      subprocess.check_call(cmd, **kwargs)
+    except subprocess.CalledProcessError as e:
+      # If the subprocess failed, it likely emitted its own distress message
+      # already - don't scroll that message off the screen with a stack trace
+      # from this program as well. Emit a terse message and bail out here;
+      # otherwise a later step will try doing more work and may hide the
+      # subprocess message.
+      print('Subprocess failed with return code %d.' % e.returncode)
+      sys.exit(e.returncode)
+    return ''
 
 
 class GclientCheckout(Checkout):