Even when volume is not persistent (like TemplateBasedVM:root), it
should be resizeable. Just the new size, similarly to the volume
content, will be reverted after qube shutdown.
Additionally, when VM is running, volume resize should affect _only_ its
temporary snapshot. This way resize can be properly reverted together
with actual volume changes (which include resize2fs call).
FixesQubesOS/qubes-issues#3519