* Wait for kube-apiserver availability before starting upgrade

I am experiencing a timing issue when upgrading from kubespray
2.11.0(k8s 1.15.3) to kubespray 2.12.6(k8s 1.16.9). The certificates get
replaced in `kubeadm-secondary-legacy.yml` and kube-apiserver notices a mismatch
(for a fraction of a second) between `apiserver.crt` and `apiserver.key`
which causes it to restart. And sometimes ( ~ 1 out of 5 upgrades) the
kube-apiserver isn't back on time for the start of the upgrade task. It
fails when kubeadm checks with the kube-apiserver to start the upgrade. The
kube-apiserver returns a `connect: connection refused`. I have created this
small task to check the availability of the kube-apiserver before starting the
upgrade, so that the upgrade will run without an issue.
Signed-off-by: Rick Haan <rickhaan94@gmail.com>

* Fix markdownlint

* Remove old CI
Co-authored-by: Maxime Guyot <maxime@root314.com>