LVM: Support efficient data copy for LVM driver

LVM: Support efficient data copy for LVM driver

The create_volume_from_snapshot() and migrate_volume() use
dd command for data copy, but the copy always copies full blocks
even if the source data contains many null or zero blocks.
When we use thin provisioned LVM, blocks are not pre-allocated,
so unused region returns zero.
If we copy full block for destination volume, unnecessary blocks
will be allocated and the usage will be 100%.

The dd command has conv=sparse option in order to copy data more
efficiently. This patch enables conv=sparse option for
create_volume_from_snapshot() and migrate_volume() when we use
thin provisioned LVM.

Change-Id: I104c4127bc4a33da9c11ad2aac93766f862e2981
Closes-bug: #1472486