Update git submodules

Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Set default volume_device_name = vdb

    refstack_defcore is currently failing on all installers.
    It will highlight the right value per installer.

    A better way is to manage the device name by a new env var set by all
    installers (it may depend on kdrive configurations)

    JIRA: FUNCTEST-947
    Change-Id: If1c12bc6798bc89136715bc78f2ac0b798e669e6
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>