qubes-rpc/admin.vm.volume.Import: fix dd flags

QubesOS/qubes-issues#2622

qubes-rpc/admin.vm.volume.Import

@@ -20,7 +20,7 @@ size=$(tail -c +3 "$tmpfile"|cut -d ' ' -f 1)
 path=$(tail -c +3 "$tmpfile"|cut -d ' ' -f 2)
 
 # now process stdin into this path
-if dd bs=4k of="$path" count="$size" iflag=count_bytes \
+if dd bs=4k of="$path" count="$size" iflag=count_bytes,fullblock \
         conv=sparse,notrunc,nocreat,fdatasync; then
     status="ok"
 else