Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Merge "xci: playbooks: provision-vm-nodes: Simplify the provision VM playbook"
  - xci: playbooks: provision-vm-nodes: Simplify the provision VM playbook

    The provision-vm-nodes playbook is only responsible for running bifrost
    to provision the XCI virtual machines. As such, drop all the extra tasks
    that this playbook performed in order to simplify it. This also drops
    the XCI_EXTRA_VARS_PATH variable since it had a rather obscure usage
    and there is not much value in passing inventory information outside of
    XCI. All these will be handled in the scenarios themselves.

    Change-Id: If5cb381a3d1e101100eb04478d80fb3045cdfaf8
    Signed-off-by: Markos Chandras <mchandras@suse.de>