Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - [centos jump] nbd build: Fix REQ_TYPE_SPECIAL

    Change-Id: Ia514418d2aae1b4f7e752d4610fa6c9829c67e51
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
    (cherry picked from commmit 84f58189f269be6633e0c8897d5624d3dfaaa650)

  - [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>
    (cherry picked from commmit 924d481ac84e8fad9bf1132e1cff18967887017e)

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 7bfb0ac..f1685ec 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 7bfb0acaea518e1ca7a64228ac5098f1bc7a9bc9
+Subproject commit f1685ec3c62fbbe1a247059c332b3b51e5db71b8