Volume moving tutorial - fixes 131

Fixes #131.

In order for tutorial to actually work #405 and #410 will need to be merged, so might want to hold off on review until those are in.
`/tmp` ran out of space for me when I ran `vagrant up`

```
Stderr from the command:

Repodata is over 2 weeks old. Install yum-cron? Or run: yum makecache fast
2014/08/04 03:08:08 Error: write /tmp/docker-export-317438209/9c1219bb985cb5ceb0a602ad943c9dd5b83cf0f16d3cd05730113fe0af37d0be/layer.tar: no space left on device
```

I changed it to /var/tmp and the vagrant build was able to complete.