Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - [docker] Cleanup, minor fixes, formula bump

    * ship prebuilt salt master conf for better readability:
      - enable x509.sign_remote_certificate (for prx VCP nodes);
    * refactor Salt master CA handling:
      - preinstall `salt_minion_dependency_packages` and
       `salt_minion_reclass_dependencies` inside docker image;
      - persistent /etc/pki;
      - run salt.minion on cfg01 to generate master keys;
    * bump container formulas to 1 Sep 2018 versions or newer:
      - inject date into Docker makefile, forcing a fresh fetch of all
        salt formulas from upstream git repos;
    * workaround broken salt-formula-designate's meta/sphinx.yml:
      - the DEB package version of salt-formula-designate uses `cmd.shell`
        to query dpkg on the minion, while the git repo version still
        uses `cmd.run`, running into parsing issues;
      - temporarily disable sphinx metadata generation for designate until
        upstream git repo syncs with the DEB version;
    * upstream: salt-formula-salt AArch64 salt.control.virt support:
      - retire salt-formula-salt git submodule and related patches;
    * skip installing reclass distro package (already installed via pip
      inside the container);
    * limit initial pillar_refresh call to nodes on jumphost;
    * remove unused salt-formula-nova git submodule;

    JIRA: FUEL-383

    Change-Id: I883b825e556f887a5e31f8a43676dcd8ece6dfde
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 57040b9..c4d91ec 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 57040b97c6317a94020ad27b8001ac0965b208f7
+Subproject commit c4d91eca1ba1614648fb2ae96340ed2876f64cd3