benchmarks: update parameters for mt-bloomfile benchmark
benchmarks: update parameters for mt-bloomfile benchmark

The old parameters were somewhat unrealistic:
- The default bloom block size is 4kb, but it was using 32kb.
- The cache capacity was set to 1MB, which meant that each shard on a
  multicore system was only 50KB or less. With the new optimization that
  allows 1% slack in MemTracker accounting, that slack was only
  500bytes or less. With 4kb bloom blocks, that optimization was
  effectively disabled.

The new parameters are slightly more realistic while keeping the
performance reasonable: 100MB cache capacity (>1MB per shard even on 88
core system) and 4kb blocks. Runtime is still reasonable - 4-5 seconds
for the query phase. The number of unique keys is bumped up to 150M to
ensure cache churn.

Change-Id: I0a85fe222285ee20d1e21ddf260cdb50c4994e96
Reviewed-on: http://gerrit.cloudera.org:8080/10242
Reviewed-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>
Tested-by: Kudu Jenkins

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