virttest: LVM storage base module

Signed-off-by: Xu Tian <xutian@redhat.com>
virttest: add lvm storage support for qemu tests

Signed-off-by: Xu Tian <xutian@redhat.com>
virttest: add emulated lvm support

Signed-off-by: Xu Tian <xutian@redhat.com>
shared.cfg: add params for supporting lvm partiton

Signed-off-by: Xu Tian <xutian@redhat.com>