Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - user-data.template: Remove salt-minion install

    salt-minion is now pre-provisioned inside the image using qemu-nbd.
    Revert "lib.sh: Limit envsubst to certain variables"

    This reverts commit 3a76d07dbd409b781abdb8520f55a1b20edf07db.
    Change-Id: Icceb8bcf439e28ab01c7731c3602c1113290454d
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
    (cherry picked from commit fac41836e91dd56696c3a435bfdbc7adf53899e2)

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index d9d2294..02a4ccc 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit d9d2294e96268012c6e1fc2239748ea49d53bbaf
+Subproject commit 02a4ccc1a0b5d8c4a708ab37066466e460c73671