Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Merge "xci: scripts: vm: Use LVM backend if available"
  - xci: scripts: vm: Use LVM backend if available

    The CI nodes come with a big secondary mechanical disk which can be
    attached directly to the clean VM. As such, we split the disk into one
    logical volume per distribution and flush the qcow2 image to it before
    attaching it to the VM. If the XCI volume group is not available, then
    we revert back to using a file-based storage backend. Finally, we hide
    stdout/stderr from the package installation process to minimize the
    script output.

    Change-Id: I11ea82899c411f8a4168e5f23cbbd8187cc891df
    Signed-off-by: Markos Chandras <mchandras@suse.de>