Update git submodules

* Update docs/submodules/sdnvpn from branch 'stable/euphrates'
  - use openstack api's instead of CLIs

    add two apis update_instance_quota_class and
    update_nw_subnet_port_quota and make run_sdnvpn_tests.py to use these
    APIs for setting quotas

    JIRA:SDNVPN-188

    Change-Id: I764bb6897e6c4c5abad4d252c1f3b4ccc742d52e
    Signed-off-by: Periyasamy Palanisamy <periyasamy.palanisamy@ericsson.com>
    (cherry picked from commit aa3ceb31df148f5ebb185271b10e4fd60fac3db1)

diff --git a/docs/submodules/sdnvpn b/docs/submodules/sdnvpn
index f4629db..21d4fce 160000 (submodule)
--- a/docs/submodules/sdnvpn
+++ b/docs/submodules/sdnvpn
@@ -1 +1 @@
-Subproject commit f4629db1b89e7a26663bd29408f2f8cd01ba68be
+Subproject commit 21d4fcefd75f42c2939820982ac7c3daa9f97c4e