Support the virtual host (cluster-wide) status health check

Since there is an HTTP API endpoint for the virtual host (cluster-wide) status [health check](https://www.rabbitmq.com/docs/monitoring#health-checks), there is no reason why `rabbitmqadmin` should not support it.

Related to https://github.com/rabbitmq/rabbitmqadmin-ng/issues/33.