Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Vagrantfile: Update base OS before installing XCI

    The Vagrant image may be old and have stale metadata leading to
    failures when installing packages. As such, it's best to update
    it as soon as possible. This is also inline with the AIO documentation
    which suggests to always use an up to date OS.

    Change-Id: I43d9f8431e1a6ed877936adc65c54be466b76aff
    Signed-off-by: Markos Chandras <mchandras@suse.de>