Update git submodules

Update git submodules

* Update docs/submodules/functest from branch 'stable/danube'
  - refstack client: improvement and fix of TestCase usage

    JIRA: FUNCTEST-772

    1, RefstackClientParser should not be a subclass of TestCase
    2, tempest_conf.py used for generating reference tempest.conf file
       not related to functest cmd, use logger is enough

    Conflicts:
        functest/opnfv_tests/openstack/refstack_client/refstack_client.py

    Change-Id: If9c37331a5a7687e5704e546efcdea8175b1529c
    Signed-off-by: MatthewLi <matthew.lijun@huawei.com>
    (cherry picked from commit 2f0b1281308cb494d83240eaa5137ca0524718b7)