[Report the #gets and #founds in db_stress]

[Report the #gets and #founds in db_stress]

Summary:
Also added some comments and fixed some bugs in
stats reporting. Now the stats seem to match what is expected.

Test Plan:
[nponnekanti@dev902 /data/users/nponnekanti/rocksdb] ./db_stress --test_batches_snapshots=1 --ops_per_thread=1000 --threads=1 --max_key=320
LevelDB version     : 1.5
Number of threads   : 1
Ops per thread      : 1000
Read percentage     : 10
Delete percentage   : 30
Max key             : 320
Ratio #ops/#keys    : 3
Num times DB reopens: 10
Batches/snapshots   : 1
Num keys per lock   : 4
Compression         : snappy
------------------------------------------------
No lock creation because test_batches_snapshots set
2013/03/04-15:58:56  Starting database operations
2013/03/04-15:58:56  Reopening database for the 1th time
2013/03/04-15:58:56  Reopening database for the 2th time
2013/03/04-15:58:56  Reopening database for the 3th time
2013/03/04-15:58:56  Reopening database for the 4th time
Created bg thread 0x7f4542bff700
2013/03/04-15:58:56  Reopening database for the 5th time
2013/03/04-15:58:56  Reopening database for the 6th time
2013/03/04-15:58:56  Reopening database for the 7th time
2013/03/04-15:58:57  Reopening database for the 8th time
2013/03/04-15:58:57  Reopening database for the 9th time
2013/03/04-15:58:57  Reopening database for the 10th time
2013/03/04-15:58:57  Reopening database for the 11th time
2013/03/04-15:58:57  Limited verification already done during gets
Stress Test : 1811.551 micros/op 552 ops/sec
            : Wrote 0.10 MB (0.05 MB/sec) (598% of 1011 ops)
            : Wrote 6050 times
            : Deleted 3050 times
            : 500/900 gets found the key
            : Got errors 0 times

[nponnekanti@dev902 /data/users/nponnekanti/rocksdb] ./db_stress --ops_per_thread=1000 --threads=1 --max_key=320
LevelDB version     : 1.5
Number of threads   : 1
Ops per thread      : 1000
Read percentage     : 10
Delete percentage   : 30
Max key             : 320
Ratio #ops/#keys    : 3
Num times DB reopens: 10
Batches/snapshots   : 0
Num keys per lock   : 4
Compression         : snappy
------------------------------------------------
Creating 80 locks
2013/03/04-15:58:17  Starting database operations
2013/03/04-15:58:17  Reopening database for the 1th time
2013/03/04-15:58:17  Reopening database for the 2th time
2013/03/04-15:58:17  Reopening database for the 3th time
2013/03/04-15:58:17  Reopening database for the 4th time
Created bg thread 0x7fc0f5bff700
2013/03/04-15:58:17  Reopening database for the 5th time
2013/03/04-15:58:17  Reopening database for the 6th time
2013/03/04-15:58:18  Reopening database for the 7th time
2013/03/04-15:58:18  Reopening database for the 8th time
2013/03/04-15:58:18  Reopening database for the 9th time
2013/03/04-15:58:18  Reopening database for the 10th time
2013/03/04-15:58:18  Reopening database for the 11th time
2013/03/04-15:58:18  Starting verification
Stress Test : 1836.258 micros/op 544 ops/sec
            : Wrote 0.01 MB (0.01 MB/sec) (59% of 1011 ops)
            : Wrote 605 times
            : Deleted 305 times
            : 50/90 gets found the key
            : Got errors 0 times
2013/03/04-15:58:18  Verification successful

Revert Plan: OK

Task ID: #

Reviewers: emayanke, dhruba

Reviewed By: emayanke

CC: leveldb
Differential Revision: https://reviews.facebook.net/D9081