[packaging]update-notifier-cds uses `udisks` command but not depending on it

[Ｖ字龍(Vdragon)]

Hi, I'm random-browsing in my Upstart user session logs(~/.cache/upstart) and found something interesting in update-notifier-cds.log:

```
六 11月 21 09:00:49 CST 2015 CD found at /dev/sdd
/proc/self/fd/9: 5: /proc/self/fd/9: udisks: not found
CD mounted at
```

It seems that update-notifier-cds tries to call `udisks` command but it fails due to Ubuntu Desktop isn't default installing that command.

### Solutions?
* It should be using the pre-installed `udisksctl` command to fetch Udisks info instead, or
* it should at least depend on udisks package for `udisks` command.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: update-notifier 0.154.1ubuntu1
ProcVersionSignature: Ubuntu 3.13.0-68.111-generic 3.13.11-ckt27
Uname: Linux 3.13.0-68-generic i686
NonfreeKernelModules: nvidia
ApportVersion: 2.14.1-0ubuntu3.19
Architecture: i386
CurrentDesktop: Unity
Date: Sun Nov 22 00:01:46 2015
InstallationDate: Installed on 2015-10-02 (50 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release i386 (20140417)
SourcePackage: update-notifier
UpgradeStatus: No upgrade log present (probably fresh install)