Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - 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>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 1815bda..fac4183 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 1815bdaf0c1765cc1fcb48031f8291409861b0b2
+Subproject commit fac41836e91dd56696c3a435bfdbc7adf53899e2