Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Pin os-odl-bgpvpn to project internal tag 6.0.0

    It is important to test and pin the versions tagged by the projects
    to ensure we have a single version of XCI with pinned versions of the
    scenarios for all the projects are recorded.

    Same exercise will be done for all the scenarios and then scenarios will
    be unpinned from the tags to let the development continue.

    deploy-scenario:os-odl-bgpvpn
    installer-type:osa

    Change-Id: I9350bc53fa87836ad36259b259edf506dd99790a
    Signed-off-by: Fatih Degirmenci <fdegir@gmail.com>