kubernetes: Manage worker nodes

So far, I have been managing Kubernetes worker nodes with Fedora CoreOS
Ignition, but I have decided to move everything back to Fedora and
Ansible.  I like the idea of an immutable operating system, but the FCOS
implementation is not really what I want.  I like the automated updates,
but that can be accomplished with _dnf-automatic_.  I do _not_ like
giving up control of when to upgrade to the next Fedora release.
Mostly, I never did come up with a good way to manage application-level
configuration on FCOS machines.  None of my experiments (Cue+tmpl,
KCL+etcd+Luci) were successful, which mostly resulted in my manually
managing configuration on nodes individually.  Managing OS-level
configuration is also rather cumbersome, since it requires redeploying
the machine entirely.  Altogether, I just don't think FCOS fits with my
model of managing systems.

This commit introduces a new playbook, `kubernetes.yml`, and a handful of
new roles to manage Kubernetes worker nodes running Fedora Linux.  It
also adds two new deploy scripts, `k8s-worker.sh` and `k8s-longhorn.sh`,
which fully automate the process of bringing up worker nodes.

roles/kubelet/files/sysctl.conf

@@ -0,0 +1,4 @@
+# Required for Kubernetes
+net.bridge.bridge-nf-call-iptables = 1
+net.bridge.bridge-nf-call-ip6tables = 1
+net.ipv4.ip_forward = 1