Better error handling in VCF Insert variants

We had "vt" dumping core, we didn't check for that an instead the VCF was empty, causing the not particularly helpful error: "Error: No split VCF records.", see below:

We should:

* Check vt has the right version (v0.57721) if not redirect to wiki
* Maybe break pipeline up into bits, so we can tell what part failed
* Check the return codes

Errors:

UploadPipeline 8969 failed. Filename: VCF - Insert variants only (no samples etc) Error: No split VCF records. This is caused by pipeline error or empty VCF after cleaning

View details in Rollbar: [https://app.rollbar.com/a/jimmy.andrews/fix/item/VariantGrid/4866](https://app.rollbar.com/a/jimmy.andrews/fix/item/VariantGrid/4866)

```
UploadPipeline 8973 failed. Filename: VCF - Insert variants only (no samples etc) Error: No split VCF records. This is caused by pipeline error or empty VCF after cleaning
```