Summary:
This patch does the following improvement for regression_test.sh
* Allow regression_test.sh to specify OPTIONS_FILE.
* Add header comments that includes examples on how to run the script
  and introduce all configurable parameters.
* bug fix.

Test Plan: Run the example commands in the header comments of regression_test.sh

Reviewers: sdong, yiwu, gunnarku

Reviewed By: gunnarku

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D59175

Summary:
This patch does the following improvement on the regression_test.sh
* allows db_bench being executed at a remost host while storing the
  benchmark results locally.
* kills all db_bench related processes before running db_bench
* better error handling.

Test Plan:
1. Run regression_test.sh both locally and remotely
2. Run multiple regression_test.sh at the same time and make sure
   i. Only one runs successfully.
   ii. The one that runs successfully will kill all other db_bench
       processes before it runs any benchmark.

Reviewers: sdong, yiwu, gunnarku

Reviewed By: gunnarku

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D58611

Summary:
This diff includes an initial script running a set of benchmarks for
regression test.  The script does the following things:

  checkout the specified rocksdb commit (or origin/master as default)
  make clean && DEBUG_LEVEL=0 make db_bench
  setup test directories
  run set of benchmarks and store results

Currently, the script will run couple benchmarks, store all the benchmark
output, extract micros per op and percentile information for each benchmark
and store them in a single SUMMARY.csv file.  The SUMMARY.csv will make the
follow-up regression detection easier.

In addition, the current script only takes env arguments to set important
attributes of db_bench.  Will follow-up with a patch that allows db_bench
to construct options from an options file.

Test Plan:
NUM_KEYS=100 ./tools/regression_test.sh

  Sample SUMMARY.csv file:

                                     commit id,                      benchmark,  ms-per-op,        p50,        p75,        p99,      p99.9,     p99.99
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,                        fillseq,      15.28,      54.66,      77.14,    5000.00,   17900.00,   18483.00
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,                      overwrite,      13.54,      57.69,      86.39,    3000.00,   15600.00,   17013.00
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,                     readrandom,       1.04,       0.80,       1.67,     293.33,     395.00,     504.00
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,               readwhilewriting,       2.75,       1.01,       1.87,     200.00,     460.00,     485.00
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,                   deleterandom,       3.64,      48.12,      70.09,     200.00,     336.67,     347.00
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,                     seekrandom,      24.31,     391.87,     513.69,     872.73,     990.00,    1048.00
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,         seekrandomwhilewriting,      14.02,     185.14,     294.15,     700.00,    1440.00,    1527.00

Reviewers: sdong, IslamAbdelRahman, kradhakrishnan, yiwu, andrewkr, gunnarku

Reviewed By: gunnarku

Subscribers: gunnarku, MarkCallaghan, andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57597