Fix migrate buffer bug.

What do these changes do?

Fix bug that migrate object fail if the object size is zero.
Fix but that vineyardd will stuck when request the same remote object twice in a short period of time.
Delete objectID from migrations map when client delete it.
Temporarily disable the kv_cache_local_file_test (This test has some problem. It will be fixed in another pr.)
Fix the wrong return value of Query function in blob storage.

Fixes #1919