spec: PDF and IDF support

spec: PDF and IDF support

XCI baremetal is a big feature which will require a lot of patches and lines of
code. Before starting the contributions, a spec will allow us to discuss and
agree on the general aspects of its architecture and implementation. That will
hopefully facilitate and increase the velocity of its reviews.

This patch provides a spec with the general design ideas for the infra_manager
tool which will allow XCI to be deployed on baremetal. Its architecture is
based on the contributions from David. All the content of the spec is questionable
even the structure of the spec :)

Change-Id: Ie4b096482c8150a04d3d3b2df0e2ca8a280aad10
Signed-off-by: Manuel Buil <mbuil@suse.com>