CA-136278: ensure '/local/domain/0/domid = 0'

This is needed for libxl functions to work. Without this expect strange
errors.

Signed-off-by: David Scott <dave.scott@citrix.com>
CA-136150: always create /var/run/xen (if it doesn't already exist)

libxl will fail to execute pygrub without this directory.

Signed-off-by: David Scott <dave.scott@citrix.com>