Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - Merge "lib.sh: Cleanup previous /boot/efi contents" into stable/euphrates
  - lib.sh: Cleanup previous /boot/efi contents

    Some UEFI firmwares insist on scanning removable drives, even when
    boot entries were deleted from UEFI boot list (board flash).

    To work around this, remove contents of </boot/efi/*>, so scanning
    won't identify any valid EFI binaries.
    Another option would be erasing partition tables, but identifying
    the underlying disk(s) is more complicated, especially when using
    LVM/RAID etc.

    Change-Id: I9949b99b139b1642e3bd8f04de3bd5ef74d1ecc5
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
    (cherry picked from commit a0a93056d5d5c52b739a2bc8fe0e2aaabb962f36)

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 2eb688d..d8508c5 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 2eb688d9bf92880107dfafd0591ee81ad8210416
+Subproject commit d8508c56661b0e0fb40e82e9feb1df1416749913