Update git submodules

Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - MaaS: Add support for dynamic fabric numbering

    Previously, we hardcoded the fabric name for our 3rd interface
    (which serves PXE/DHCP for the target nodes) to "fabric-2",
    relying on predictable index numbers to be provided by MaaS based
    on the interfaces defined in /etc/network/interfaces.

    However, the fabric IDs/names generated by MaaS are not predictable,
    and therefore cannot be hardcoded in our reclass model / scripts.

    Work around this by:
    - adding support for fabric ID deduction based on CIDR matching
      during subnet create/update operation in MaaS py module;
    - adding support for VLAN DHCP enablement to MaaS py module,
      which was previously handled via shell MaaS API operations
      from maas/region.sls;

    While at it, revert previous commit that disabled network discovery
    ("MaaS: Disable network discovery"), since it turns out that network
    discovery was not the culprit for subnet creation failure, but wrong
    fabric numbering.

    This reverts commit 8cdf22d1a1bae4694a373873cab4feb6251069b7.

    Change-Id: I15fa059004356cb4aaabb38999ea378dd3c0e0bb
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>