Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Fixing SDNVPN tempest API tests

    The code to run Tempest tests has changed in SDNVPN between Euphrates
    and Fraser, causing these tests to fail. Moreover, due to a bug in
    SDNVPN, not all bgpvpn API tests are currently being run. This is being
    addressed by https://gerrit.opnfv.org/gerrit/#/c/57299/ and needs to be
    cherrypicked to Fraser 6.1 for inclusion in OVP 2.0.

    Change-Id: I0a7575e8a9ebc23af5edaa26c1a9ce1e8149919c
    Signed-off-by: Georg Kunz <georg.kunz@ericsson.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index 191f86a..931c730 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit 191f86a9713b857e9d3047a972fa6f8c8aca6c59
+Subproject commit 931c730ff814959c16f07405ba98ca5158c8f326