GCE shell branch work, November 2013 through now

Roughly speaking:

- Oldest four commits, through commit 25d20d1b6f5f424c2c59b346019874dce5c639e7, line up with the debian-cloud images dated 20131120 and (backports kernel) 20131127, which are current and were published in connection with Google Compute Engine general availability. This includes:
    - Rename old image_bundle tool to gcimagebundle
    - Add support for --use-backports-kernel true, to pull in the backports kernel and set up apt_preferences to prefer it. (Courtesy of my colleague @HimanshuVasishth)
- @rybaktomasz added support for using the host environment's NTP server. Not only is this a best practice in virtual environments, it allows time sync for GCE instances configured without external connectivity.
- Work around the hostname.sh issue for GCE instances. (Courtesy of my colleague @jeremyje)