Update git submodules

Update git submodules

* Update docs/submodules/sdnvpn from branch 'master'
  - os-odl-bgpvpn scenario for xci deployment

    This includes scenario os-odl-bgpvpn scenario specific configuration
    files to make XCI to install Openstack (master and stable/pike) with
    OpenDaylight configured as a BGP speaker.
    XCI would automatically checkout sdnvpn repo and use scenarios
    directory for the configuration during its execution time.

    Change-Id: Ic86fcb171c8e97f7d3c3fb649ab0fb00368e6c6d
    Signed-off-by: Periyasamy Palanisamy <periyasamy.palanisamy@ericsson.com>