Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - [patch] Fixup ceilometer server publisher default

    - backport proposed fixup for ceilometer;
    - remove 'ignore: all' from .gitmodules to make it easier to bump the
      submodule;
    - bump system submodule to upstream latest;
    - drop patch merged upstream;

    JIRA: FUEL-350

    Change-Id: I68f232e0da5af368a1669a7379eedde5c4168b84
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 86e9d8d..4608ea7 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 86e9d8de2e3174438c5e640e0bd27d59d003126b
+Subproject commit 4608ea751ebbe43479e60215599eae506fd3b963