[cern] Update k8s to 1.5.2

Following up the cherry-pick for k8s 1.4.7 [1] and fix for docker-storage-setup [2], update k8s version to 1.5.2.

[1] https://gitlab.cern.ch/cloud-infrastructure/magnum/commit/280096fce4053579b4baf1c4808a6aecd95af054 [2] https://gitlab.cern.ch/cloud-infrastructure/magnum/commit/eb5cd5186fcbb9a7e505c2a40e09bcd25b242e0c