Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - [maas] Download only used subarches images

    - reduce download size/time for MaaS images by downloading only the
      subarch images we use;
    - fix stop condition in MaaS artifact download script;
    - stop importing images before updating the boot resources to prevent
      race conditions;

    Change-Id: I3b15fae3463bc6c54be2cc06e0cb31edcbd307cb
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index dfe0808..7f797f1 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit dfe08086ac3d02a921bdd5cb3e52865396f1d774
+Subproject commit 7f797f1b5a9340d24d700879abca6b39413e7375