Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - Add documentation for scenarios

    Added documents for feature scenarios supported by fuel.
    The nofeature scenarions don't require documentation.

    Change-Id: I574e42b60125b4a59c8d921fa45e4c4fbf09137f
    Signed-off-by: Cristina Pauna <cristina.pauna@enea.com>
    (cherry picked from commit 2a74900ecd451c939a34d53a529e802cc2250db9)

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 2c4241c..52e2e55 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 2c4241c3d04ac1e5f43c701e776ae37684681e63
+Subproject commit 52e2e55bf55b58a304553fe1529def3709c91ded