Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - bifrost: Ensure OS images are present in the PXE directory

    The XCI deployment script may wipe the PXE directories so we need
    to place the OS images after this has happened so we don't download them
    every time.

    Change-Id: Iccf943bc75592e7f5dddea59dfee14b2b080e7ef
    Signed-off-by: Markos Chandras <mchandras@suse.de>

diff --git a/docs/submodules/releng-xci b/docs/submodules/releng-xci
index e668471..20b01a6 160000 (submodule)
--- a/docs/submodules/releng-xci
+++ b/docs/submodules/releng-xci
@@ -1 +1 @@
-Subproject commit e66847184999a84c472648e78d71e12b7c5b23d2
+Subproject commit 20b01a6b7163971201a5aa0d6db354d80657d17f