Presubmits failing due to lint

[jlewi]

Presubmits are failing due to lint issues and a bug in the code.

Here's the bug.

Your code has been rated at 9.79/10
Traceback (most recent call last):
 File "/usr/lib/python2.7/runpy.py", line 174, in _run_module_as_main
   "__main__", fname, loader, pkg_name)
 File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
   exec code in run_globals
 File "/mnt/test-data-volume/kubeflow-tf-operator-presubmit-tfjob-e2e-402-21ef552-66-26e1/src/kubeflow/tf-operator/py/py_checks.py", line 202, in <module>
   main()
 File "/mnt/test-data-volume/kubeflow-tf-operator-presubmit-tfjob-e2e-402-21ef552-66-26e1/src/kubeflow/tf-operator/py/py_checks.py", line 198, in main
   args.func(args)
 File "/mnt/test-data-volume/kubeflow-tf-operator-presubmit-tfjob-e2e-402-21ef552-66-26e1/src/kubeflow/tf-operator/py/py_checks.py", line 54, in run_lint
   failed_files.append(full_path.strip[len(args.src_dir):])
TypeError: 'builtin_function_or_method' object has no attribute '__getitem__'

The bug is only triggered if a lint issue occurred.

The lint issues started because the docker image used by the tests got rebuilt which caused us to switch to using python3.

The lint issues are specific to python3.