NOTE: This patch would modify all Backend's data.
And this will cause a very long time to restart be.
So if you want to interferer your product environment,
you should upgrade backend one by one.
1. Refactoring be is to clarify the structure the codes.
2. Use unique id to indicate a rowset.
Nameing rowset with tablet_id and version will lead to
many conflicts among compaction, clone, restore.
3. Extract an rowset interface to encapsulate rowsets
with different format.
Class definition of ByteBuffer duplicates between olap/byte_buffer.h and util/byte_buffer.h.
All of the two classes has a function names as remaining().
Some place which want to call remaining() of util/byte_buffer.h is linked to the other remaining() function of olap/byte_buffer.h
