Optimize the usage of fs benchmark tool:
1. Remove `Open` benchmark, it is useless.
2. Remove `Delete` benchmark, it is dangerous.
3. Add `SingleRead` benchmark, user can specify an exist file to test read operation:
`sh bin/run-fs-benchmark.sh --conf=conf/hdfs_read.conf --fs_type=hdfs --operation=single_read`
4. Modify the `run-fs-benchmark.sh`, remove `OPTS` section, use options in `fs_benchmark_tool` directly
5. Add some custom counters in the benchmark result, eg:
```
--------------------------------------------------------------------------------------------------------------------------------
Benchmark Time CPU Iterations UserCounters...
--------------------------------------------------------------------------------------------------------------------------------
HdfsReadBenchmark/iterations:1/repeats:3/manual_time/threads:1 6864 ms 2385 ms 1 ReadRate=200.936M/s
HdfsReadBenchmark/iterations:1/repeats:3/manual_time/threads:1 3919 ms 1828 ms 1 ReadRate=351.96M/s
HdfsReadBenchmark/iterations:1/repeats:3/manual_time/threads:1 3839 ms 1819 ms 1 ReadRate=359.265M/s
HdfsReadBenchmark/iterations:1/repeats:3/manual_time/threads:1_mean 4874 ms 2011 ms 3 ReadRate=304.054M/s
HdfsReadBenchmark/iterations:1/repeats:3/manual_time/threads:1_median 3919 ms 1828 ms 3 ReadRate=351.96M/s
HdfsReadBenchmark/iterations:1/repeats:3/manual_time/threads:1_stddev 1724 ms 324 ms 3 ReadRate=89.3768M/s
HdfsReadBenchmark/iterations:1/repeats:3/manual_time/threads:1_cv 35.37 % 16.11 % 3 ReadRate=29.40%
HdfsReadBenchmark/iterations:1/repeats:3/manual_time/threads:1_max 6864 ms 2385 ms 3 ReadRate=359.265M/s
HdfsReadBenchmark/iterations:1/repeats:3/manual_time/threads:1_min 3839 ms 1819 ms 3 ReadRate=200.936M/s
```
- For `open_read` and `single_read`, add `ReadRate` as `bytes per second`.
- For `create_write`, add `WriteRate` as `bytes per second`.
- For `exists` and `rename`, add `ExistsCost` and `RenameCost` as `time cost per one operation`.
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