Cleanup command-line argument building

[dleehr]

The KubernetesJobBuilder.container_args method builds up a simple command-line array connecting stdout, stdin, and stderr.

This method should address the same concerns as cwltool's JobBase._execute, doing the following:

• [x] check if directories for redirected file exist
• [x] command-line quoting
• [ ] ShellCommandRequirements
• [ ] Secrets