Update git submodules

Update git submodules

* Update docs/submodules/sdnvpn from branch 'master'
  - Merge "Clean up stale routers and gateway routers."
  - Clean up stale routers and gateway routers.

    During snaps_smoke test all floating IPs are allocated
    by routers as external IP's, as a result there are no
    more floating IPs left.
    This patch clean up stale routers and free the assigned
    IPs.

    JIRA: SNAPS-318

    Change-Id: Ifbf01ce38db63315e692dca9ffa5d993dbfa4337
    Signed-off-by: dimitris.tsiolakis <dmts@intracom-telecom.com>