MB-27420 CouchRocks: Set data block size to 16KB
MB-27420 CouchRocks: Set data block size to 16KB

Performance tests and analisys of the RocksDB statistics have shown that
the default data block size of 4KB for SST file is sub-optimal.
Given the results of the analisys at MB-27420, we set the default data
block size to 16KB.

Change-Id: I0d4d1fcf29e613f1f53617e41e5607883fd613c6
Reviewed-on: http://review.couchbase.org/88242
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Daniel Owen <b3fc0e1a51f252986e60be7da121b74d3ac6845f@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine