Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Leverage on pbr (Python Build Reasonableness)"
  - Leverage on pbr (Python Build Reasonableness)

    pbr can inject requirements into the install_requires, tests_require
    and/or dependency_links arguments to setup.

    It finishes cleaning the requirements management [1] for all OPNFV
    projects integrated by Functest.

    [1] https://wiki.opnfv.org/display/functest/Requirements+management

    Change-Id: I30b76db8dcaba809e0b314fbd06ae04d24c8baca
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>