Fix links broken by openstack-manuals file move

Several files were moved out of openstack-manuals/doc/common
with Change-Id Iacd5c68c639e60e8c711cb18351543e477444299, which broke
building in training-guides.

This patch fixes the broken links and makes training-guides build again.

Change-Id: I6863041e5c4e1a53f68629ca810ad812cf82bf02