Build full Xen distribution.
Changes since v4:
* Removed "opts=" from xencommons init script.
* Backported upstream patch to boot Syslinux PV-DomUs with pygrub
(allows booting Alpine PV-DomUs).
Changes since v3:
* Added bash as a runtime dependency, since some hotplug scripts
use that instead of /bin/sh.
Changes since v2:
* Clean and updated init scripts to be as similar as possible to
upstream version.
Changes since v1:
* Removed net from xencommons dependencies and added udev.
