Delete AWS Resources step sometimes fails if job is cancelled

[willdavsmith]

Sometimes, if the Test Samples workflow runs and is cancelled, something will cause the "Delete AWS Resources" step to get stuck in an infinite loop and cancel:

We could try adding the cancelled() condition here or making resource cleanups part of a different job.

AB#11549

[ytimocin]

I updated this step to only run if the Deploy App step is successful and if Cancel Workflow is not called.

[ytimocin]

Continuing the discussion here: #1009.