Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Merge "bifrost: Bump bifrost SHA"
  - bifrost: Bump bifrost SHA

    Bump the bifrost SHA so we can get rid of the testvm.xml.j2 template
    which has now made it upstream.

    Change-Id: Ia9cdd999a5702f37125d38e0ba68bb31920d2117
    Signed-off-by: Markos Chandras <mchandras@suse.de>

diff --git a/docs/submodules/releng-xci b/docs/submodules/releng-xci
index 4b9f7b3..53d1b25 160000 (submodule)
--- a/docs/submodules/releng-xci
+++ b/docs/submodules/releng-xci
@@ -1 +1 @@
-Subproject commit 4b9f7b3f892486a8ea721aa72bed573db298fa69
+Subproject commit 53d1b2596cc1b416aeec2f154bd1c5329cb04ee9