Change the default cache size and write batch size
Change the default cache size and write batch size

- Change the default cache size and write batch size to 128 MB and
10, respectively, when there bench_config.ini doesn't exist.

couchbaselabs/ForestDB-Benchmark,couchbaselabs/ForestDB-Benchmark,yyangpan/ForestDB-Benchmark,yyangpan/ForestDB-Benchmark,yyangpan/ForestDB-Benchmark