Annoying put block failure log

[zjshen14]

We have two code path that a block could be appended to the blockchain: 1) consensus module commits a block after reaching consensus; 2) block sync receives a block from peers. The race condition could happen between the two path. However, it should not matter if a block has been put successfully already, and the second put fails because the block exists already. We need to catch the error on both side and check the error type. If the error is that block exists already, we shouldn't log an error