Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Merge "bifrost: Set vCPU model to 'host-passthrough'"
  - bifrost: Set vCPU model to 'host-passthrough'

    The default CPU model of QEMU GenuineIntel/QEMU Virtual CPU is not the
    best option for vCPU in terms of performance. As such, lets use the
    real host CPU. This has also been submitted upstream and the template
    should be removed once the upstream patch has been merged and the SHA
    for bifrost is bumped.

    Change-Id: I23d86933604c290d5650b73f420972d0a2b23dc8
Link: https://review.openstack.org/#/c/528677/
    Signed-off-by: Markos Chandras <mchandras@suse.de>