`--single-process` does not apply inherited requirements and hints

[jdidion]

Running a single process with --single-process should still cause all requirements/hints inherited from the step and its ancestors to be applied. Running env-wf2 conformance test as follows causes the workflow-level requirement to be ignored:

cwltool --single-process step1 env-wf2.cwl env-job.yml

[jdidion]

This does fix #1531. It only fixes #1530 for non-packed workflows.