Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - Merge "Set volume_device_name variable"
  - Set volume_device_name variable

    This evironment variable is required by test suite to refer
    to an attached volume (vdb is reserved for config drive).

    JIRA: FUEL-353
    Change-Id: I4f7c96b2344575fcd9b785e3c74b27ef4c4d64f8
    Signed-off-by: Michael Polenchuk <mpolenchuk@mirantis.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index a12266c..8bd6edd 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit a12266c64987be03998ee9ad663a691fd8b58134
+Subproject commit 8bd6edd252ca5e8f62ef24ae27fe4c8123ec82f7