Pyflakes warnings

The pyflakes code checkers reports the following about the code:

```
./pickleshare.py:43: 'os' imported but unused
./pickleshare.py:316: local variable 'data' is assigned to but never used
./pickleshare.py:325: undefined name 'test'
./pickleshare.py:326: undefined name 'stress'
```

Of those, the first is probably just a line to remove.

For the second, that's more annoying: I would say something is defined as "data" then used as "db"... when db unfortunately does exist! So it might be an actual bug.

The last two are as far as I see something to remove because it's a non-existing feature.