Fixes <xi:include> and removes <xi:fallback>
Fixes <xi:include> and removes <xi:fallback>

Changes the location point <xi:include> to git.openstack.org
as it is a more reliable source for OpenStack projects.

Change-Id: I014e4ce2f5e97f22b206b02e2b8b3af93da6d18b
Partial-Bug: #1338678

openstack/training-guides,harrisonfeng/training-guides,Nabs007/training-guides,Nabs007/training-guides,openstack/training-guides,Nabs007/training-guides,harrisonfeng/training-guides,harrisonfeng/training-guides