Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - [virtual] Bring in OpenDaylight DPDK scenario

    Change-Id: If77ac85fa86e0a1a18c0cc2abff77d876cdb9e93
    Signed-off-by: Michael Polenchuk <mpolenchuk@mirantis.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 4fae473..421aa57 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 4fae473d4343f78facda713b5626b47d3dd33e9c
+Subproject commit 421aa5796c194382bec24737b9b1d60bde544672