Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Fix Expermental JJB Job Diff Commenting"
  - Fix Expermental JJB Job Diff Commenting

    This change fixes the following issues:
    1) 'nounset' will cause the script to fail when activating a virtualenv
       since the activation of a virtualenv unsets variables
    2) There are not artifacts available from releng-merge-jjb and copying
       them would save minimal time over re-running jjb

    Change-Id: Ifc4297947c8fe235987a507ead932841480165a7
    Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>