deploy fails with no error details when using kustomize with invalid manifests/arguments

### Expected behavior
skaffold should surface errors encountered running `kubectl` to the user
### Actual behavior
skaffold just prints `exit status 1` and exits when it is unsuccessful running `kubectl kustomize ...`

### Information

- Skaffold version: 2.4.1
- Operating system: WSL ubuntu
- Installed via: APT
- Contents of skaffold.yaml:

```yaml
apiVersion: skaffold/v4beta4
kind: Config
manifests:
kustomize:
paths:
- abc
deploy:
kubectl: {}
```

### Steps to reproduce the behavior

Run `skaffold deploy` with the above file in an otherwise empty directory. skaffold just prints `exit status 1` and exits with no other error details.

Running with `-v trace` shows that it tried to run `kubectl --context ... kustomize abc`, running that gives the real error message which should have been returned by skaffold:
```
error: must build at directory: not a valid directory: evalsymlink failure on '/home/mike/skaffold_repro/abc' : lstat /home/mike/skaffold_repro/abc: no such file or directory
```