Knowing that Atlassian supports only single instance of JIRA on self host, that is, you can only have one JIRA instance running in one Tomcat container, how does Atlassian run its own OnDemand? Does Atlassian have a "special" build of JIRA that's multitenant? Or does Atlassian spin up a seperate "instance" everytime a new client signs up as <companyname>.atlassian.net?