Passing open files (stdin) to Singularity different from Docker

## Expected Behavior
CWL v1.1 conformance test 199 (stdin_shorcut) should work on both Docker and Singularity

#1378
## Actual Behavior
Passes on Docker, with output:
```
16 198 1111
```

Fails on Singularity with output:
```
16 198 1111
```

This must is some difference in the passing of filehandles as the code in `job._job_popen` is basically identical.

NB: Running the commands in a shell in the singularity container can get the "correct" answer:
```
Singularity> wc < cwl-v1.1-main/tests/whale.txt
16 198 1111
Singularity> cat cwl-v1.1-main/tests/whale.txt | wc
16 198 1111
```
Singularity> cat cwl-v1.1-main/tests/whale.txt | wc

For now, I'm disabling this test for singularity, but it should be enabled.

See also #1378