fix bug 1110521 - only use peep for installing dependencies, not setup.p...

...y

r? @peterbe @selenamarie 
If you have time, perhaps something more elaborate.
```
We strongly prefer to confidently install dependencies with 
`peep install -r requirements.txt` before we do anything, but
if we list the dependencies here, setuptools will forcibly pip install
all the dependencies (with the dependencies) when you run
`python setup.py install` which we need so that socorro becomes 
a package that can be imported. 
```