fix bug: failed create empty volume when kvmHostAddons.qcow2Options is null
fix bug: failed create empty volume when kvmHostAddons.qcow2Options is null

zstackio/zstack-utility,zstackio/zstack-utility,zstackorg/zstack-utility,zstackio/zstack-utility,zstackorg/zstack-utility,zstackorg/zstack-utility