kubicle: Update default k8s version to 1.8.4
kubicle: Update default k8s version to 1.8.4

This commit updates the default version of k8s used by kubicle.  There was a
race condition in the old default version, that could cause kubeadm to fail
randomly.

Signed-off-by: Mark Ryan <f16215f7acd0bd7fdc465539215bd574c785b062@intel.com>

ciao-project/ciao,kaccardi/ciao,ciao-project/ciao,kaccardi/ciao,01org/ciao,01org/ciao