Update git submodules

Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Update juju_epc to leverage on new scenarios

    It avoids duplicating codes across all OPNFV testcases.

    It also fixes the issues when starting mongodb [1] by upgrading juju agent.
    It stops supporting keystone v2 as the other testcases.

    [1] https://build.opnfv.org/ci/view/functest/job/functest-compass-baremetal-daily-master/lastFailedBuild/console

    Change-Id: I06cddddef1121292ffb695dcb73aa79a07c23192
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>