ObjectStore Test: Add test for simulating scrub behavior

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
KeyValueStore: Fix scrub causing inconsistence state

Fix #8589
Backport #Firefly
Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
Merge pull request #2430 from yuyuyu101/kvstore-scrub-inconsistence

Kvstore scrub inconsistence

Reviewed-by: Sage Weil <sage@redhat.com>