Update git submodules

Update git submodules

* Update docs/submodules/sdnvpn from branch 'master'
  - potential fix for attaching router with external network gateway

    In the CI environment, whenever testcases attaches a router with
    external network gateway sometimes it throws the error "No more IP
    addresses available on network". This could be due to stale floating
    ip's exist in the deployment which is cleaned up now before executing
    sdnvpn testsuite.

    JIRA: SDNVPN-212

    Change-Id: I027a833f13b1bdddd83dc8c7e7f7292e20b10bb8
    Signed-off-by: Periyasamy Palanisamy <periyasamy.palanisamy@ericsson.com>