Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - Merge "[virtual] Setup nfs for nova instances"
  - [virtual] Setup nfs for nova instances

    Configure nfs shared storage for nova instances
    to support live migration feature.

    Change-Id: I777d5725e45d03325507d3ecc8dd59a28cbc188f
    Signed-off-by: Michael Polenchuk <mpolenchuk@mirantis.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 06d34f4..6d90d3b 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 06d34f4086f0dcc515b6db0eab3fdeb2d15de640
+Subproject commit 6d90d3be1fbb7526587a305167e3295bc956d5d4