terraform: specify the cpu to kvm64 by default
Using the null value to use the default proxmox value is not
working. The host
value is restored on the state after a refresh
if it's not forced to kvm64.
Related to T3795
The configuration was manually done on proxmox and will be apply on the next vm reboots
Test Plan
terraform refresh
terraform plan
Migrated from D6845 (view on Phabricator)