Templates do not count towards a user's quota and cannot be started.
Staff owners may mark and unmark their VMs as templates, so a staff
user could mark a VM as a template, use the freed quota elsewhere, and
unmark it again: the VM came back without any check, over the quota.
For users with a quota (everyone but superusers), turning a template
back into a VM now passes check_user_quota with the VM's size (one VM,
its vCPUs, memory and disks). If the quota is reached or cannot be
verified, it stays a template and the user is told why. Marking a VM as
a template frees quota and is not checked. The view takes the
per-user quota lock like the other quota-checked changes.
The existing template-flag test gives its mocked VM a size. The new
tests fail on the previous code.
