Xpand nodes must be added one by one to the cluster as an attempt
to add more nodes will fail, if any of the nodes to be added
already are in the cluster.
Further, the adding of a node may also fail if, when the addition
is made, the addition of the previous node is still in process.
Now it will be attempted at most 5 times, while sleaping as many
seconds between each attempt as there has been attempts.
Some additional logging was also added.
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