Switch to top frame when capturing settings in the tearDown

This is addressing issue #434.

Settings can only be captured by privileged apps and thus failures hosted apps like marketplace do not teardown nicely.

Solution is to switch to the top level frame. There are no repercussions of this because all following steps in the teardown are not specific to the app.

A test case to replicate the teardown failure against is:
```
self.apps.launch('Marketplace')
assert 1 == 2
```

@davehunt r?