[rocksdb] Regression tests

Summary:
* Fixed regression test params by @dhruba's suggestion
* Added p50, p75 and p99 to regression metrics

Test Plan: build_tools/build_regression_test.sh

Reviewers: dhruba, emayanke

Reviewed By: dhruba

CC: leveldb, dhruba, reconnect.grayhat

Differential Revision: https://reviews.facebook.net/D14355
Fix typo.
Merge pull request #18 from isamu/doc_typo_fix

Fix typo.
Set background thread name with pthread_setname_np()

Summary: Makes it easier to monitor performance with top

Test Plan: ./manual_compaction_test with `top -H` running.  Previously was two `manual_compacti`, now one shows `rocksdb:bg0`.

Reviewers: igor, dhruba

Reviewed By: igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14367
Don't do compression tests if we don't have compression libs

Summary: These tests fail if compression libraries are not installed.

Test Plan: Manually disabled snappy, observed tests not ran.

Reviewers: dhruba, kailiu

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14379
Readrandom with small block cache

Summary: Added readrandom benchmark with 300MB block cache, while database has 1GB of data

Test Plan: Ran it

Reviewers: dhruba, MarkCallaghan

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14373