Update git submodules

Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - [baremetal] Add upstream (lab) proxy support

    If upstream proxy is defined in IDF, propagate it to pillar data:
    - linux:system:proxy:keyserver:http(s) for cfg01, mas01;
    - maas:region:upstream_proxy for mas01;

    Sample IDF config:

    idf:
      fuel:
        network:
          upstream_proxy:
            address: 10.0.2.2
            port: 3128

    JIRA: FUEL-317

    Change-Id: I12be815e1b4564227fb09c20ce06cd71e7d433b6
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>