xci: Enable node provisioning and shuffle/rename stuff

This change enables node provisioning using bifrost based on the chosen
flavor.

Other changes include
- move flavor specific stuff (playbooks, inventory, vars) into their own
folders so it is easier to copy them over.
- rename flavors and get rid of xci from them.
- introduce env-vars to keep variables that are not really user variables.

Please note that this patch contains empty files and so on due to still
trying to find best way to structurei things. Apart from this, there will
probably be lots of duplications here and there which will be taken care
of once things settle.

Change-Id: I04a5d422e5b018439bafea5e68e65255ae38d22b
Signed-off-by: Fatih Degirmenci <fatih.degirmenci@ericsson.com>