Fix workbench for IPython 6

._update_indent() was changed not to take arguments and IPython.core.usage.quick_guide was removed.

In test_execute_async_returns_failure_on_runtime_error_and_captures_expected_stack the comment was causing an IndentationError, changing it to a docstring fixes the problem. I don't think this is related to IPython but probably a python 3.6 problem.