Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  to a15c6cb8fc93125d025a462c40b9961bb969e9ec
  - Merge "[armband] Cleanup Fraser jobs, sync with Fuel"
  - [armband] Cleanup Fraser jobs, sync with Fuel

    - retire Fraser stream;
    - sync Dovetail jobs with Fuel jobs;
    - retire virtual deployments (haven't been used in a long time, for
      manual testing, Fuel generic jobs can be triggered on ARM virtual
      pods if needed);
    - s/gambia/hunter/g, but keep them disabled for now;
    - use Fuel's job templates in Armband definitions;
    - prepare for merging the Armband jobs with Fuel jobs;

    Change-Id: I0b0a3106248603e510cd6e9646da267777ddc572
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>