镜像压缩倍(以512mb计算)
img:1
qcow:0.000003904104232788
qcow2:0.000366225838661193
vdi:0.000004768371582031
vhdx:0.015625
vmdk:0.000244140625
hd:0.000061988830566406
vhd:0.000005722045898437
注意:img占的空间太大不适合分享，除了小镜像外
仅适合自己测试