Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - xci: infra: bifrost: Set XCI_DISTRO if it's not defined

    The XCI_DISTRO variable is normally set from the XCI deployment script.
    However, on bifrost jobs, we don't run this script as part of XCI so we
    need to ensure that this variable is set properly.

    Change-Id: I295b65176bab6ccbdd12aa50449d3c021a88b43d
    Signed-off-by: Markos Chandras <mchandras@suse.de>

diff --git a/docs/submodules/releng-xci b/docs/submodules/releng-xci
index 88fc810..eeb906a 160000 (submodule)
--- a/docs/submodules/releng-xci
+++ b/docs/submodules/releng-xci
@@ -1 +1 @@
-Subproject commit 88fc810539b0ecc6ffd74cd3de88de527221938c
+Subproject commit eeb906a553d6ddf70ffc5af1acadb33a13ff5990