@Override
        public String toString() {
            return "failure path: " + failureReason + " upon removing " + hostsCausingFailure;
        }
Contains the list of hosts that, upon being removed, caused an unrecoverable state,
as well as the specific host and tenant which caused it.
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/CapacityChecker.java