Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - Merge "[centos jump] Add missing dependency for nbd build" into stable/euphrates
  - [centos jump] Add missing dependency for nbd build

    Change-Id: Icb23d2e6d3bb6e49b54e2d51cc8a35cb03702fcd
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
    (cherry picked from commit 60e790a986e64a47f4242766500f1aee6a3083ed)

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 17b63ba..15cc7c3 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 17b63ba2c2f40b5b8995280d5f2cb4e696246402
+Subproject commit 15cc7c371020cf860f3d19318e6dc5af31eea5d6