Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Adapt Functest E release Framework

    Use opnfv/functest-restapi:euphrates.
    Adapt Functest E framework for all Functest test cases.
    1. All path of functest and sdnvpn has been changed.
    2. Sdnvpn can clean resources by itself with E release, no need to clean again.
    3. Add a file testcases.yaml to overwrite the file in functest container,
       then it can support to run tempest_custom i.e. ipv6 and tempest in OVP.

    JIRA: DOVETAIL-584

    Change-Id: I3ba9aa8e80becaa99cc89c8db4b39acbb89dfda4
    Signed-off-by: xudan <xudan16@huawei.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index ff2a7b3..c4131f9 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit ff2a7b3f7de37e64164250b8fa9a623dd061bac5
+Subproject commit c4131f9a18b9e9eaee75e6e1503d34d6678115a2