Petsc conifg opts changed

@hajgato: correct me if I'm wrong, but this is just an unrolled version of the loop in the `else` part, but with `BLACS` excluded?

If so, we should rework this to:

```python
deps = ["FFTW", "ScaLAPACK"]
if LooseVersion(self.version) < LooseVersion("3.5"):
    deps.append("BLACS")

# loop in else part over 'deps'
```