Update git submodules

Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - MaaS: Fix missing service.maas.cluster.single inc

    Upstream change [1] made the inclusion of service.maas.cluster.single
    mandatory by using some default reclass definitions which we don't
    override explicitly.

    [1] https://github.com/salt-formulas/salt-formula-maas/commit/
        ce118a238bae4bcf19d2f10bca591a40405f7c3c

    Change-Id: I5746b6906b341a7257e0cd2b4b0bed8ea25840f4
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>