The guest kernel requires more memory depending on how many disks are
attached. 256 seems to be enough for basically any reasonable and
unreasonable amount of disks though.
For debug instance, make it 1G, as these are never started automatically
anyway, and need at least 512MB since the initramfs (especially when
including a debug build of the daemon) is substantially bigger.
Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>