Bug 1847197

Cause: The DNS operator was changed in OpenShift 4.2.13 to remove a blanket toleration for all taints from the operator's operand. This change was made in order to prevent the operand from being scheduled to a node before the node's networking was ready. Consequence: Adding arbitrary taints to nodes could cause problems related to the DNS operator's operand. For one, adding a NoSchedule taint to nodes could lead to alerts' being raised for operand pods that were already running on the newly tainted nodes. For another, taints could prevent the operand from running on a node. The operand needs to run on every node in order to add the cluster image registry's host name and address to the node host's /etc/hosts file. Without this entry in /etc/hosts, the node's container runtime could fail to pull images from the image registry, breaking upgrades and user workloads. Fix: The toleration for all taints has been restored for the DNS operator's operand. The operand also has a node selector to ensure that it runs only on Linux nodes. Result: The operand runs on, and it updates /etc/hosts on, all Linux node hosts. "Missing CNI default network" events may be observed when the operand starts on a node that is still initializing, but such errors are transient and can be ignored.