HDDS-7607. [Snapshot] SnapshotDiff command lists unmodified file as modified

[sadanand48]

What changes were proposed in this pull request?

Fix issue which shows key as modified

bash-4.2$ ozone sh volume create vol1
bash-4.2$ ozone sh bucket create vol1/buck1
bash-4.2$ ozone sh key put vol1/buck1/key1
bash-4.2$ ozone sh snapshot create vol1/buck1 snap1
bash-4.2$ ozone sh snapshot create vol1/buck1 snap2
bash-4.2$ ozone sh snapshot snapshotDiff vol1/buck1 snap1 snap2
Difference between snapshot snap1 and snapshot snap2:
M key1

Also fixed snapdiff for FSO buckets

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-7607

How was this patch tested?

Added Basic Snapdiff unit tests

[smengcl]

Thanks @sadanand48 for the fix and test addition!