Adding Cloud DNS

@proppy - here you go.

Tail end of my build test and verification...

```sh
...
    | Cloud SDK for Go Developers                 |     1 |          |
    | Cloud SDK for Java Developers               |     1 |          |
    | Cloud SDK for Python and PHP Developers     |     1 |          |
    ------------------------------------------------------------------

Do you want to continue (Y/n)?  
Creating update staging area...


Installing: App Engine SDK for Go (Linux, x86_64) ... Done
Installing: App Engine SDK for Java ... Done
Installing: App Engine SDK for Java (Platform Specific) ... Done
Installing: App Engine SDK for Python and PHP ... Done
Installing: Cloud SDK for Go Developers ... Done
Installing: Cloud SDK for Java Developers ... Done
Installing: Cloud SDK for Python and PHP Developers ... Done

Creating backup and activating new installation...

Done!

 ---> 490d02ee6d8f
Step 7 : RUN mkdir /.ssh
 ---> Running in 51f41243e65e
 ---> 3824a355746d
Step 8 : ENV PATH /google-cloud-sdk/bin:$PATH
 ---> Running in 3e748a126e1b
 ---> fd754cc824fd
Step 9 : VOLUME ["/.config"]
 ---> Running in 04086768ab92
 ---> e22ad1f23848
Step 10 : CMD bash
 ---> Running in df446976e3d2
 ---> d63846089979
Successfully built d63846089979

erjohnso@docker$ docker run -t -i d638 /bin/bash
root@164ad9ee8503:/# gcloud components update

All components are up to date.
root@164ad9ee8503:/# gcloud components list
The following are the components available through the Google Cloud 
SDK.  You may choose to install one or more of the pre-configured 
packages (which contain everything you need to get started), and/or 
any of the individual components below.

---------------------------------------------------------------------------
|                                Packages                                 |
|-------------------------------------------------------------------------|
| Status    | Name                                    | ID         | Size |
|-----------+-----------------------------------------+------------+------|
| Installed | Cloud SDK Core Command Line Tools       | pkg-core   |      |
| Installed | Cloud SDK for Go Developers             | pkg-go     |      |
| Installed | Cloud SDK for Java Developers           | pkg-java   |      |
| Installed | Cloud SDK for Python and PHP Developers | pkg-python |      |
---------------------------------------------------------------------------


-------------------------------------------------------------------------------------------
|                                  Individual Components                                  |
|-----------------------------------------------------------------------------------------|
| Status        | Name                                   | ID                  |     Size |
|---------------+----------------------------------------+---------------------+----------|
| Not Installed | Developer Preview gcloud Commands      | preview             |   < 1 MB |
| Installed     | App Engine SDK for Go (Linux, x86_64)  | gae-go-linux-x86_64 |  31.9 MB |
| Installed     | App Engine SDK for Java                | gae-java            | 147.6 MB |
| Installed     | App Engine SDK for Python and PHP      | gae-python          |  35.9 MB |
| Installed     | BigQuery Command Line Tool             | bq                  |   < 1 MB |
| Installed     | Cloud DNS Admin Command Line Interface | dns                 |   < 1 MB |
| Installed     | Cloud SDK Core Libraries               | core                |   < 1 MB |
| Installed     | Cloud SQL Admin Command Line Interface | sql                 |   < 1 MB |
| Installed     | Cloud Storage Command Line Tool        | gsutil              |   1.8 MB |
| Installed     | Compute Engine Command Line Tool       | gcutil              |   < 1 MB |
-------------------------------------------------------------------------------------------

To install new components or update existing ones, run:
 $ gcloud components update [component ids]
root@164ad9ee8503:/# 
```