Update git submodules
* Update docs/submodules/functest from branch 'master'
- Pull functest-core when only building childs
Otherwise it fails if parent and childs containers are not built on
the same host [1].
It would have worked if the docker images were correctly cleant. Then
the last image would have been pulled.
[1] https://build.opnfv.org/ci/job/functest-apex-baremetal-daily-euphrates/362/console
Change-Id: I293829c839c1cf68c9f7668aa643e16889359fcc
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>