Fix configure_containerd.sh script idempotency
Created by: matofeder
Script configure_containerd.sh did not evaluate whether the containerd file is already present in the cluster-template.yaml. Hence, the file could be added on each script execution.
This commit adds a check which evaluates whether the containerd file is already present in the cluster-template.yaml. This makes configure_containerd.sh idempotent.
Closes #471 (closed)