ENG-4856: Bound the number of buffers used for decompression in
StreamSnapshotDataReceiver.

The StreamSnapshotDataReceiver now takes a FixedDBBPool that contains a fixed
number of direct byte buffers. It will take buffers from this pool for both
compressed data and decompressed data.
Merge pull request #593 from VoltDB/ENG-4856-clean

ENG-4856: Bound the number of buffers used for decompression in StreamSnapshotDataReceiver