Update git submodules

Update git submodules

* Update docs/submodules/sdnvpn from branch 'stable/gambia'
  - Fix false message instance is down

    JIRA: SDNVPN-238
    JIRA: SDNVPN-232

    This patch fixes the false message instance is down. The message
    occurs because a wrong method was used to check if instance is
    alive. This instance does not proceed to login so the previous
    method cound not find "login" regex inside its console output.

    Change-Id: I35733f634595a9d2eeb9148c2476444afab710a6
    Signed-off-by: Stamatis Katsaounis <mokats@intracom-telecom.com>
    (cherry picked from commit eea8b6c296f7c9540de7f46bc9daaee9e1e14ae5)