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>

diff --git a/docs/submodules/releng-xci b/docs/submodules/releng-xci
index 6b0d1b5..8b9a73d 160000 (submodule)
--- a/docs/submodules/releng-xci
+++ b/docs/submodules/releng-xci
@@ -1 +1 @@
-Subproject commit 6b0d1b52fd82839e2d7d7e450dcae662368703c5
+Subproject commit 8b9a73d7fbc9bf6112b7efbbb2ad7f3216837ba4