[hotfix][coordination] Reduce log level for suppressed failures from …

…WARN to DEBUG.

Suppressed failures happen when the coordinator is receiving a fail() call while it is already
undergoing a failure/recovery cycle. This happens relatively frequently because of follow-up
errors triggered by the fact that the coordinator is undergoing failover.

This was previously logged with WARN level, we change it to DEBUG, because these follow-up errors
are not something that should alert the user, they are usually not relevant at all. We only output
them on DEBUG level for debugging cases.

flink-runtime/src/main/java/org/apache/flink/runtime/operators/coordination/OperatorCoordinatorHolder.java

@@ -542,7 +542,7 @@ public OperatorID getOperatorId() {
  public void failJob(final Throwable cause) {
  checkInitialized();
  if (failed) {
- LOG.warn(
+ LOG.debug(
  "Ignoring the request to fail job because the job is already failing. "
  + "The ignored failure cause is",
  cause);