PlainTableFactory::PlainTableFactory() to have huge TLB turned off by default

Summary: PlainTableFactory::PlainTableFactory() now has Huge TLB page feature turned on by default. Although it is not a public API (which we always turn the feature off now), our unit tests, like db_test sometimes uses it directly, which causes wrong coverage of codes. This patch fix it to allow unit tests to run with the correct setting

Test Plan: Run db_test and make sure this feature is not on any more.

Reviewers: igor, haobo

Reviewed By: igor

CC: yhchiang, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D18483
log_and_apply_bench on a new benchmark framework

Summary:
db_test includes Benchmark for LogAndApply. This diff removes it from db_test and puts it into a separate log_and_apply bench. I just wanted to play around with our new benchmark framework and figure out how it works.

I would also like to show you how great it is! I believe right set of microbenchmarks can speed up our productivity a lot and help catch early regressions.

Test Plan: no

Reviewers: dhruba, haobo, sdong, ljin, yhchiang

Reviewed By: yhchiang

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18261