Navigation to sub workflow tasks doesn't work in some cases

[rakhmerov]

Below is a example of a workbook (can be uploaded with 'mistral workbook-create wb.yaml') which is not handled well by CloudFlow. If we navigate to the first task (sub_wf1) of 'top_level_wf' we'll see that its task properties are not displayed correctly on the right. And back navigation doesn't seem to work after that as well (or may be works very slowly).

version: '2.0'

name: demo_wb
description: This is the workbook for the Sprint Demo

workflows:
  # Top level workflow
  top_level_wf:
    tasks:
      sub_wf1:
        workflow: sub_wf1
        on-success: sub_wf2

      sub_wf2:
        workflow: sub_wf2
        on-success: sub_wf3

      sub_wf3:
        workflow: sub_wf3

  # 2nd level workflows
  sub_wf1:
    tasks:
      t1:
        workflow: sub_wf1_sub_wf

  sub_wf2:
    tasks:
      t1:
        action: std.noop

  sub_wf3:
    tasks:
      t1:
        action: std.noop

  # 3rd level workflows
  sub_wf1_sub_wf:
    tasks:
      t1:
        action: std.noop

(GuyShaanan: update to preserve yaml syntax highlight)