Introduction of PDF/IDF

Introduction of PDF/IDF

this is a proposition of self sufficient PDF/IDF to describe the POD
where XCI is running.

The PDF [Pod Description File] is describing the physical
level of the POD where XCI will run the installer. It lists servers and
their description (CPU/RAM/DISK/NICS)

The IDF [Installer Description File] is describing how the installers
will use the POD. 2 sections are today important in this IDF:
- idf.net_config is describing the network topology
- xci section is set to describe how common steps (network, nfs,
  ceph,...) of XCI will use the pod.

Another section of IDF idf.[installer], curretnly empty, will
contain all pod specificities that are linked to an installer (osa,
kolla, k8s,...) and not shared with the others.

Those 2 files are describing the vitual pod as it is already
deployed by the XCI. Those default files can be replaced by the ones
describing the target pod (done manually or with the CI). It would then
be to the install process to take into account these files (to be done).

Change-Id: I3dcbd965f8c84b03d34eb0fd68599d7bec402dbd
Signed-off-by: Blaisonneau David <david.blaisonneau@orange.com>