Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - [centos jump] Add nbd build support

    RHEL distros do not maintain nbd, so add a best-effort function
    to build it on the fly.

    Change-Id: Ie0419f0fed8a0b12f6b878b3093d6ca34f72d140
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 52e73b6..924d481 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 52e73b648550fb8f3549af690d579a503a982ecf
+Subproject commit 924d481ac84e8fad9bf1132e1cff18967887017e