public static HostRemovalFailure create(Node host, Node tenant, AllocationFailureReasonList failureReasons) {
            return new HostRemovalFailure(Optional.of(host),
                                          Optional.of(tenant),
                                          failureReasons);
        }
Data class used for detailing why removing the given tenant from the given host was unsuccessful.
A failure might not be caused by failing to allocate a specific tenant, in which case the fields
will be empty.
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/CapacityChecker.java