[cern] Upgrade to Fedora Atomic 25

Cherry-pick: https://review.openstack.org/#/c/417457/8

Image contains:
kubernetes-1.4.7-1.fc25.x86_64
docker-1.12.5-4.git03508cc.fc25.x86_64
flannel-0.5.5-8.fc25.x86_64
etcd-3.0.15-1.fc25.x86_64

* For this upgrade the upstream image is used, which is
  uploaded here [1].
* Minor changes for flannel and docker-storage-setup
  were needed.
* The image will be built in the CI and uploaded to
  tarballs.openstack.org as soon as possible.

[1] https://fedorapeople.org/groups/magnum/fedora-atomic-25-20161221.qcow2

Change-Id: Iac6e30c530821a49a5c3978e335e0b1d56a576e0

Conflicts:
	magnum/drivers/common/templates/fragments/configure_docker_storage_driver_atomic.sh
	magnum/drivers/common/templates/kubernetes/fragments/write-network-config.sh
	magnum/drivers/k8s_fedora_atomic_v1/version.py
	magnum/drivers/swarm_fedora_atomic_v1/version.py
	magnum/tests/contrib/gate_hook.sh