fix bug 880899 - Show only mozhacks on the homepage

https://bugzilla.mozilla.org/show_bug.cgi?id=880899

To test:

1.  Within admin, create a feed for moz-hacks (if you don't have one already) using  http://hacks.mozilla.org/feed/

2.  Create a bundle for said feed called "updates-moz-hacks"

3.  ./manage.py update_feeds

Now the homepage should just feature hacks content.