In some (most) cases VM needs to be started to complete resize
operation. This may be unexpected, so make it clear and do not start the
VM when the user did not explicitly allow that.
FixesQubesOS/qubes-issues#1268
1. Do not start GUI session - to reduce startup time
2. Use user="root" instead of sudo - not all templates have sudo
installed (for example fedora-21-minimal)
3. Add missing wait=True - otherwise VM may be shutdown during the
operation.
QubesOS/qubes-issues#1268