pep8 improvements on bok-choy tests.

@jzoldak @muhammad-ammar @clytwynec 
I feel like a better way to resolve this is to break the logic up:
```python
if is_calibrating:
    css_selector = "input.calibration-interstitial-page-button"
else:
    css_selector = "input.interstitial-page-button"
self.q(css=css_selector).first.click()
```