Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Switch to OPNFV Fraser release

    1. Use Functest Fraser docker images whose tag is fraser
    2. Use Yardstick stable docker images
    3. Functest fraser has moved testcases.yaml file from functest/ci to xtesting/ci
    4. Functest fraser has removed 'functest env prepare' command
    5. Functest uses rally to execute osinterop test cases
       instead of refstack_client

    Change-Id: I81ebefe6ea959ca77c2c87f1d75ef56ac18c165f
    Signed-off-by: xudan <xudan16@huawei.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index 749946d..13877a0 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit 749946dcc5b17cfca43c6e8692359f4972e48b21
+Subproject commit 13877a00e5155ee93bb4255a81e104c1ebf1f11e