:tenant is an API param for the compute resources which is used by Openstack. AzureRM uses tenant too as a parameter for creating the compute resource. However, AzureRM will be a plugin compute resource and although updating params of a resource is possible, but it has some limitations. It cannot modify the existing params, but it can add new ones.
So, I think we can just add a simple line in the description String "For Openstack and AzureRM only"