Update git submodules

Update git submodules

* Update docs/submodules/armband from branch 'stable/danube'
  - docs: Experimental features note about ceilometer

    Starting with Danube.1.0, Ceilometer and MongoDB are experimental
    in upstream Fuel@Openstack, so the appropiate feature group needs
    to be enabled during master node installation to use them.

    Change-Id: Ib522c7e81cc73625128296873b4f9eef7cf1e99d
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
    (cherry picked from commit 6aea8823d25b049f47ea0ebceb04269427e9c0e3)