Update git submodules

Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Merge "Define create_snapshot() and clean() in TestCase"
  - Define create_snapshot() and clean() in TestCase

    They replace the former calls in run_tests which are not suitable for all
    test cases. Now any test case can define how to clean its resources.

    If the snapshot cannot be created, the test case is considered as
    failed. Only a message is printed if any failure during cleaning.

    It also defines a new class called OSGCTestCase useful for test cases
    which don't clean their OpenStack resources.
    All test cases located in opnfv_tests/openstack inherit from it to
    keep the global behavior unchanged.

    It also deletes exit instructions in openstack_clean and
    openstack_snapshot, removes clean flags in testcases.yaml and updates
    the related utils.

    All Docs are modified as well.

    JIRA: FUNCTEST-438

    Change-Id: I8938e6255708012380389763a24059ace4ce45d8
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>