Update git submodules

Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - Merge "[baremetal] PDF: Use net_admin for MaaS PXE net" into stable/euphrates
  - [baremetal] PDF: Use net_admin for MaaS PXE net

    While at it, fix another small issue where a variable
    (parameters__param_opnfv_maas_pxe_address) was used without being
    populated (defined in 'runtime.yml', which is not read using
    `parse_yaml`, like the scenario yml or the PDF expanded class,
    pod_config.yml).

    JIRA: FUEL-313

    Change-Id: Iee88601d5420f55572bf90c8cf330afbedfb2e21
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
    (cherry picked from commit 9136aef95f77a1f26175929caedfe6ae662bbbd8)