Skipping when exit code has failed for workflow custom tests.

[rhpvorderman]

With #153 most tests are now skipped if the exit code fails, which makes the output much easier to read. This does not affect the custom tests however. Since the condition is only known after workflow runtime this might be very hard to implement without changing when the workflows run. Also custom tests only give the workflow name so have no knowledge of the workflow objects involved in order to check the exit code.

[sstrong99]

this would also be useful for me