<fix>[vm]: add lsof check before umount memory snapshot
<fix>[vm]: add lsof check before umount memory snapshot

Resolves: ZSTAC-47683

Change-Id: I7a6d6e696e6d65716961727a6962776576676f73

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