Improve snapshot verification in VM policy after adding new client

Rather than checking all clients again after adding new clients to a VMware backup policy it would make sense to only check the newly added clients. Checking all clients in the policy takes unnecessarily and excruciating long (in my case between 30 to 45 minutes, depending on amount of clients in the policy), during which time the NBU console is locked for other tasks. Alternatively you could give customers the option to switch this check off. Most of us check the eligibilty of the VM client anyway before we add it to a VM policy.