Adds a local Autoupdate server and a mechanism for adding developer packages.

I've been getting frustrated by juggling usb sticks to constantly update my netbook so I wrote a simple
server that can run in a developer's source tree and serve updates to a netbook. I also added an upstart
task that will download a script from the dev server and run it. I use this to install sshfs, gdb, and vim.

Here's a quick heads up about what has changed. 

1. /etc/lsb-release

I added two new fields to the release file. One is the URL that should be pinged for updates. The other is the URL that can be used to download a developer setup script. 

2. chromeos_version.sh

The functionality for the release build is unchanged, however, developer builds now have a monotonically increasing version number. 

3. software-update.conf

Autoupdate is disabled when the DEV_SERVER field in /etc/lsb-release is initialized. This field won't be set on the build server, but will be set everywhere else. 

4. ping_omaha.sh

The omaha server is now configured by /etc/lsb-release

Review URL: http://chromereview.prom.corp.google.com/1175098

git-svn-id: svn://chrome-svn/chromeos/trunk@92 06c00378-0e64-4dae-be16-12b19f9950a1
tree: 4b825dc642cb6eb9a060e54bf8d69288fbee4904

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