StoreTest: Add clone xattr test

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
GenericObjectMap: sync transaction avoid lookup_parent failed

Now rm_keys after clone in one transaction will lead to "lookup_parent"
in rm_keys failed because of nonexisting parent header.

We need to sync clone transaction in advance.

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
KeyValueStore: Make clone error message more friendly

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
KeyValueStore: Add clone op detect to promote error

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
Merge pull request #2710 from yuyuyu101/keyvaluestore-clone-rmattr

Fix Keyvaluestore clone rmattr