Provide way to not start LogSyncer thread

In our usecase we want all the Mutations on all the tables to be immediately written and synced to WAL. We dont want the LogSyncer thread to be running in such a case.

In minbatch operation we write entries to WAL and we use postWALWrite and write some more WAL entries(Only write no sync). We want all these written data to be synced as one unit (at the sync step in doMiniBatchOperation) But if the LogSyncer thread is running in the system it can come and do the sync at any point in time which we dont want in our case.