Add the ability to lease one of a set of well-known test tenants

[mwadams]

In order to deal with limitations around the rate of creation and deletion of resources, it is sometimes necessary to use pre-existing infrastructure for tests.

In order to ensure that you can use existing infrastructure in a tenanted scenario, you need to use well-known tenant IDs.

To avoid contending those resources, we need to provide a leased "round robin" approach to acquiring tenants on a store.