Improve error message when container is not available

## Expected Behavior
Docker is available, but container is not.

## Actual Behavior

```
Error response from daemon: manifest for biocontainers/interproscan:latest not found
Workflow error, try again with --debug for more information:
Docker is not available for this tool, try --no-container to disable Docker, or install a user space Docker replacement like uDocker with --user-space-docker-cmd.: Command '['docker', 'pull', 'biocontainers/interproscan:latest']' returned non-zero exit status 1.
```

Would be nice to tell user what exactly is wrong. In this case there is no latest container

Start by reproducing the reported docker pull failure for biocontainers/interproscan:latest and trace where cwltool turns that failure into the workflow error. Done means the message distinguishes an unavailable container tag from Docker itself being unavailable and gives the user actionable guidance.

Written by the indexing model from the issue text.