Fixes: Building docker in Virtualbox fails

Building docker in virtualbox fails since the machine has not enough memory. 

Error: 
```
sudo docker run -privileged -v `pwd`:/go/src/github.com/dotcloud/docker docker 

---> Making bundle: binary (in bundles/0.7.0-dev/binary)
# github.com/dotcloud/docker/docker
collect2: ld terminated with signal 9 [Killed]
```