By definition StandaloneVM is not linked to the template. Creating one
from a template is a clone operation. It's already possible using
qvm-clone tool, but it's logical to do that using qvm-create tool too.
This was the case in R3.2 too.
While adding this special case, skip cloning private volume, to preserve
behaviour of TemplateBaseVMs which do not inherit private volume either.
FixesQubesOS/qubes-issues#3793
If file to be imported is larger than the default root volume, resize
the volume first. It might be also a good idea to shrink it when needed,
but currently the backend refuse it.
FixesQubesOS/qubes-issues#3422
