Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "jjb: xci: Use centos-minimal instead of centos7 element"
  - jjb: xci: Use centos-minimal instead of centos7 element

    The full distro elements are not well maintained. Upstream OpenStack
    also prefers the minimal elements when building images for the CI so
    we should do the same to minimize the delta between the two systems.

    Change-Id: Ifeddb0a74c2434df2cfa95cde36b4aaac1516698
    Signed-off-by: Markos Chandras <mchandras@suse.de>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 11a3323..8a0f2be 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 11a33235be45d9562d4a77487b6318a3dbd83f4f
+Subproject commit 8a0f2beba8bd91c4ac395be08293841fc2b29426