Support extra arguments in kfctl_e2e_workflow.py

* See kubeflow/testing#489 we want to support having run_e2e_workflow.py
  pass extra arguments to the workflow. To do that we need to update the
  test to first accept unknown arguments so we don't break once
  run_e2e_workflow.py starts adding extra arguments.

py/kubeflow/kubeflow/ci/kfctl_e2e_workflow.py

@@ -74,7 +74,8 @@ def __init__(self, name=None, namespace=None,
                test_endpoint=False,
                use_basic_auth=False,
                build_and_apply=False,
-               kf_app_name=None, delete_kf=True,):
+               kf_app_name=None, delete_kf=True
+               **kwargs):
     """Initialize a builder.
 
     Args: