Container entrypoint - fix CWL conformance test docker-run-cmd.cwl supporting containers with entrypoint set

[fabricebrito]

When the container has an entrypoint, the pod command is malformed, see https://github.com/Duke-GCB/calrissian/blob/master/calrissian/job.py#L232-L233:

spec:
  containers:
  - args:
    - -c 'echo '"'"'moo'"'"' > cow'
    command:
    - /bin/sh
    - -c

Here's the conformance test: https://github.com/common-workflow-language/cwl-v1.2/blob/main/tests/docker-run-cmd.cwl

Calrissian conformance test failure log: https://github.com/Duke-GCB/calrissian/blob/master/conformance/results-v1.2.txt#L652-L659