Apparently it is much faster. Especially during savefile preparation -
tar reads the whole file, while bsdtar gets file map and reads only used
regions.
It have nothing to do with xenstore, so change the name to not mislead.
Also get rid of unused "xid" parameter - we should use XID as little as
possible, because it is not a simple task to keep it current.
Move DispVM creation to qfile-daemon-dvm/QubesDisposableVm from
qubes-restore. As actual restore is handled by libvirt, we don't get
much from separate qubes-restore process.
This code still needs some improvements, especially on performance.
Opening a DispVM when the TemplateVM is running forces savefile
regeneration. Checking real root.img modification time (taking into
account root-cow.img) is tricky, so display a warning instead.
