Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - Merge "[virtual] Reset mtu for compute management bridge"
  - [virtual] Reset mtu for compute management bridge

    Use default mtu for br-mgmt in order to resolve the live
    migration failure (cannot recv data: connection timed out)

    Change-Id: I9cee453d87f849e29fc877fff237f8e604f2df53
    Signed-off-by: Michael Polenchuk <mpolenchuk@mirantis.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index a10b771..fa63bf2 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit a10b7711ab3d400830406a2c425acb3431b4a5c1
+Subproject commit fa63bf2a6afe2c2139ae9161fd995d54df70fd68