prototypes: xci: Add ability to use local repositories for testing

prototypes: xci: Add ability to use local repositories for testing

When developing XCI features it's useful to be able to use the local
repositories rather than cloning them from git since that makes
it harder to test local modifications against XCI. As such, we add
three new variables which can be used to hold local paths to the
bifrost, releng and openstack-ansible repositories. We are still
cloning the repositories but we then use the 'synchronize' Ansible
module to copy modified files from the local repositories.

Change-Id: I6d593ea48d8b9c51415d9d0848f77a498ef2f486
Signed-off-by: Markos Chandras <mchandras@suse.de>