i have a request to upgrade ESXi host that is currently a 2 host cluster. this cluster is managed via vCenter 6.5 and the hosts are currently running 5.5. i need to upgrade both host and the customer would like to not have any downtime during the upgrade if possible. my question is, can i load all VM's onto one host, upgrade from 5.5 to 6.5 then migrate all VM's off the 5.5 host to the 6.5 host without powering them down. will the vm hardware allow me to hot migrate a vm from a 5.5 host to a 6.5