Currently `dvc run -p angles` is broken when you use it with `params.yaml`
that looks like this:
```
angles:
- 2
- 3
- 100
- 3.2
- 36.2
- 3.6
```
because we are incorrectly using `flatten` instead of simply using some
xpath-like library to access params that are specified.
Ruslan Kuprieiev
9de8d1e0fa