Update git submodules

Update git submodules

* Update docs/submodules/functest from branch 'stable/danube'
  - refstack client: manually running improvement

    JIRA: FUNCTEST-758

    1.python tempest_conf.py can generate a reference tempest.conf under /hom/opnfv/.../refstack_client
      this is based on "rally verify configure-verifier"
      surely, user can define his/her own tempest.conf by not using this
    2.python refstack_client.py -c <tempest_conf_path> --testlist <testlist_file_path>
      if not given, will use default path, if file not exists, will have error

    Change-Id: I1ceecbe8fe86fbe0d53b736a0f3b9a9ae01f262f
    Signed-off-by: MatthewLi <matthew.lijun@huawei.com>
    (cherry picked from commit 678d5f956b1af373f61f97187ff3e66fdb315654)