Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - states: maas: Stop using maas-stable PPA

    Currently, Xenial repos provide MaaS 2.2.x, while the PPA bumped it
    to 2.3.x. Since we switched to 2.3, we observed a rare wrongful state
    transition from 'Deploying' back to 'Ready'.
    Drop the PPA, falling back to 2.2 from mainline distro repos.

    JIRA: FUEL-312

    Change-Id: I3daa118059f37cbeca076da685661c28f3a28a97
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
    (cherry picked from commit 9da33bc85d681950a09452f28ca39df2108b0b56)

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 08bde71..d616588 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 08bde71385047eefcd7ac6aa211df5a83c145bdb
+Subproject commit d6165887af0b6c9d2024a17e7f4cc8039ca761ab