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.
Apparently it doesn't work with some kernels - saved domain still needs
original memory amount to restore successfully. This happens at least on
3.12.14 kernel.
Because qfile-daemon-dvm always requests 400MB from qmemman, this change
should harm anyone - in any case DispVM needs 400MB free memory to
start.
Note that "xl mem-set" line is still there, which makes savefile somehow
smaller (so faster restore).
