PipReq and VirtualenvReq need to fail if their package installation fails

If the installation of packages fails for any reason, the Req needs to fail also. Here what happens currently on a timeout while trying to download a package:

```
File "/usr/lib/python2.7/socket.py", line 447, in readline
     data = self._sock.recv(self._rbufsize)
timeout: timed out
Storing complete log in /home/ubuntu/.pip/pip.log
[OK]
```

The Req returns that [OK] and continues on.
