Nova-compute and sparse lvm volumes does not work as expected

Detailed bug description:

We use lvm backed storage on compute nodes using settings:

images_type=lvm
images_volume_group=vm

We want to switch into sparse volumes with 'sparse_logical_volumes = True' setting.
If we use just sparse volumes on existing VG, then we have an error.

Steps to reproduce:

add the following lines in /etc/nova/nova.conf or /etc/nova/nova-compute.conf on a compute node.

[libvirt]
images_type=lvm
images_volume_group=vm
sparse_logical_volumes = True

restart nova-compute service.

Expected results:
Instances will be created sparse logical volumes in LVM group vm.

Actual result:
nova show <is>
http://paste.openstack.org/show/510464/

Log files:
http://paste.openstack.org/show/510466/

Reproducibility:
MOS 7.0

The reason of the error:
Logical volume has been created with 64 MB (as described preallocated size)
https://github.com/openstack/nova/blob/master/nova/virt/libvirt/storage/lvm.py#L62

# lvs
  /dev/vm/27a4f366-92fb-4991-a364-51c9d363c88c_disk: read failed after 0 of 4096 at 21474770944: Input/output error
  /dev/vm/27a4f366-92fb-4991-a364-51c9d363c88c_disk: read failed after 0 of 4096 at 21474828288: Input/output error
  /dev/vm/27a4f366-92fb-4991-a364-51c9d363c88c_disk: read failed after 0 of 4096 at 0: Input/output error
  /dev/vm/27a4f366-92fb-4991-a364-51c9d363c88c_disk: read failed after 0 of 4096 at 4096: Input/output error
  LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert
  root os -wi-ao--- 442.52g
  swap os -wi-ao--- 4.00g
  27a4f366-92fb-4991-a364-51c9d363c88c_disk vm swi-I-s-- 64.00m [27a4f366-92fb-4991-a364-51c9d363c88c_disk_vorigin] 100.00

LVM documentation shows that thing volumes should be created by the command:
It is also possible to create both the thin pool as well as the logical volume inside the thin pool in one command:

lvcreate -T <volume group>/<thin_pool> -V <size> -L <preallocated size> -n <name>

Nova-compute creates sparse disk using the following command:
https://github.com/openstack/nova/blob/master/nova/virt/libvirt/storage/lvm.py#L75-L76