Fix link for training-cluster-scripts
Fix link for training-cluster-scripts

Currently we link to a copy of the scripts on docs.openstack.org - and
that location does not exist.

Instead of putting this data on docs.openstack.org, let's give a
reference to github and distribute it from there.

Change-Id: I4dc7f31a3a50520ccef16db7e4ff0b54d02d89ff
Closes-Bug: #1282874

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