Standardize repository locations

* The variables pointing to repositories were not using the GIT_BASE for
github.com
* Some repositories were missing the .git tail

Change-Id: I551179bed90c04682e8a22985241a4bddca23351
Small Refactors

Rename TOP_DIR to THIS_DIR, change the order of variable definitions.

Change-Id: I96c12c5102e658ec76ab5176c3207fb641dae078
XenAPI: run DomU on a virtual kernel

Fixes bug 1154506.

Change-Id: I6e2f576a6de19db70f2a88278f9c043a433f4cec