Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - xci: playbooks: Add task for loading distribution variables

    vars_files doesn't support loading files with variables in their names.
    As such we add a new task to include these files before running any of
    the roles. This fixes warnings like this:

    Info: Starting provisining VM nodes using openstack/bifrost
    -------------------------------------------------------------------------
    No config file found; using defaults
    skipping vars_file '../var/{{ ansible_os_family }}.yml' due to an undefined variable
    skipping vars_file '../var/{{ ansible_os_family }}.yml' due to an undefined variable
    skipping vars_file '../var/{{ ansible_os_family }}.yml' due to an undefined variable
    skipping vars_file '../var/{{ ansible_os_family }}.yml' due to an undefined variable
    skipping vars_file '../var/{{ ansible_os_family }}.yml' due to an undefined variable
    skipping vars_file '../var/{{ ansible_os_family }}.yml' due to an undefined variable

    Change-Id: I0a49e2ed8d811bb40a99612462752f8691133e0f
    Signed-off-by: Markos Chandras <mchandras@suse.de>