util/cedarish: Update apt sources
util/cedarish: Update apt sources

This is the list of sources used by the Ubuntu Core image with the
universe lines uncommented.

Check with:

```
$ URL="https://partner-images.canonical.com/core/trusty/20170330/ubuntu-trusty-core-cloudimg-amd64-root.tar.gz"

$ curl -fsSL "${URL}" | tar xzO etc/apt/sources.list | grep -oP 'deb .*$' | grep -vP '(backports|multiverse)'
deb http://archive.ubuntu.com/ubuntu/ trusty main restricted
deb http://archive.ubuntu.com/ubuntu/ trusty-updates main restricted
deb http://archive.ubuntu.com/ubuntu/ trusty universe
deb http://archive.ubuntu.com/ubuntu/ trusty-updates universe
deb http://archive.ubuntu.com/ubuntu/ trusty-security main restricted
deb http://archive.ubuntu.com/ubuntu/ trusty-security universe
```

Signed-off-by: Lewis Marshall <748e1641a368164906d4a0c0e3965345453dcc93@lmars.net>

lmars/flynn,flynn/flynn,philiplb/flynn,lmars/flynn,philiplb/flynn,philiplb/flynn,flynn/flynn,flynn/flynn,philiplb/flynn,flynn/flynn,flynn/flynn,lmars/flynn,lmars/flynn,lmars/flynn,philiplb/flynn