Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - Merge "base image: Explicitly call kpartx"
  - base image: Explicitly call kpartx

    qemu-nbd currently available in CentOS 7 does not add partition
    mappings automatically for NBD devices, so add explicit `kpartx`
    calls.

    Change-Id: Ifa79c89b82024602b782c449dbf4de10899e03b5
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index b51c5f3..2050647 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit b51c5f365f80cbad9f96d1c1c2c471a2d148414e
+Subproject commit 2050647bd70043be2eb90a45b7173a25570b8c8d