Specifying a custom container path does not work.

```
vscli open -b force-container -c /home/me/projects/vscli/.devcontainer/devcontainer.json /workspace/vscli/tests

Error:
   0: Path /workspace/vscli/subfolder does not exist

Location:
   src/workspace.rs:86

Backtrace omitted. Run with RUST_BACKTRACE=1 environment variable to display it.
Run with RUST_BACKTRACE=full to include source snippets.
```

Does not work.