Update git submodules

Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Bugfix: Dovetail tool will crash when hosts.yaml file with incorrect format

    If the hosts.yaml file is like,
    —
    hosts_info:
    192.168.141.101:

    it will raise an exception,
    File "/usr/local/lib/python2.7/dist-packages/dovetail/utils/dovetail_utils.py",
    line 227, in add_hosts_info
    names=hostnames)
    File "/usr/local/lib/python2.7/dist-packages/python_hosts/hosts.py",
    line 54, in _init_
    raise Exception('Address and Name(s) must be specified.')
    Exception: Address and Name(s) must be specified.

    If the hosts.yaml file is empty, it will crash with,
    File "/usr/local/lib/python2.7/dist-packages/dovetail/container.py",
    line 174, in create
    if hosts_yaml['hosts_info']:
    TypeError: 'NoneType' object has no attribute '_getitem_'

    JIRA: DOVETAIL-621

    Change-Id: I547928e514b3294c048379459c07df89879fbb03
    Signed-off-by: xudan <xudan16@huawei.com>