Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Merge "xci: scripts: vm: Use virtio for disk and network I/O"
  - xci: scripts: vm: Use virtio for disk and network I/O

    This ensures that the virtio paravirtualization driver is used for both
    disk and network I/O which should provide the best performance since we
    no longer need to emulate a real bus or driver.

    Change-Id: Ic46a38f51b06cb4b848d87d890d23fec022b2f15
    Signed-off-by: Markos Chandras <mchandras@suse.de>