Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Create dovetail-docker-build-stable job"
  - Create dovetail-docker-build-stable job

    1. Dovetail first release is based on OPNFV danube release.
    2. Dovetail has the branch stable/danube now.
    3. It needs to automatically triggle dovetail-docker-build-stable job
       when there is a patch cherry picked to this stable branch.

    JIRA: DOVETAIL-576

    Change-Id: I58a639cd8208e40099c6481085d1f450c89b2523
    Signed-off-by: xudan <xudan16@huawei.com>