We currently have CUCM 6.1.5 and it is upgradeable to 8.6. I want to setup a test environment for migrating our 6.1.5 database over to 8.6 for testing. However, when I go to download/order the software from the Product Upgrade Tool it only states the upgrade software. I take it I cannot install a standalone 8.6 installation as it would require me installing 6.1.5 and then upgrading. Is this correct?