Add support for installing kubernetes cluster via devstack.
It uses kubeadm to bootstrap the k8s cluster.
Change-Id: I7877ceda08bbdab807116a13d74ff884136dc501
There are several projects that tried to install docker in different
ways. This potentially lead to failure of more than one such services
were enabled. This commit consolidate docker installation into
a devstack plugin so that other services could depend on it.
The initial script was mainly from Kuryr-libnetwork. Kuryr, Fuxi,
and Zun might leverage this script to install Docker in the future.
Change-Id: I97dbff2f361acc98b12ec6f40ab115c8548477a3
