Multiple properties are related to system installed inside the VM, so it
makes sense to have them the same for all the VMs based on the same
template. Modify default value getter to first try get the value from a
template (if any) and only if it fails, fallback to original default
value.
This change is made to those properties:
- default_user (it was already this way)
- kernel
- kernelopts
- maxmem
- memory
- qrexec_timeout
- vcpus
- virt_mode
This is especially useful for manually installed templates (like
Windows).
Related to QubesOS/qubes-issues#3585
af2435c0d4