In order to make the etcd instances of the VMs join into a single cluster,
we used to use the discovery mechanism.
This made the cluster bootstrap dependent on an external etcd cluster instance.
74601ea replaced the dependency on discovery.etcd.io by a local etcd cluster.
This change completely gets rid of the dynamic discovery mechanism in favor
of the static configuration method.
This should be both safe and light since it completely removes the need of having
an external etcd cluster running somewhere (either discovery.etcd.io, or locally).
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