a tool like mysqlslap implement in golang

useage:

 mysqlslap  -Hhost -uuser -ppassword -P3306 -ddatabase -q"select id from deviceattr where name='attr10' or name='attr20' group by id;" -ffilename -c 50 -i 100

输出报告：

Summary:
 Name:         mysqlslap
 Count:        40
 Total:        1.01 s
 Slowest:      1.00 s
 Fastest:      1.01 s
 Average:      1.00 s
 Requests/sec: 39.76

Response time histogram(ms):
 1003.000 [1]  |∎∎
 1003.300 [0]  |
 1003.600 [0]  |
 1003.900 [0]  |
 1004.200 [24] |∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎
 1004.500 [0]  |
 1004.800 [0]  |
 1005.100 [12] |∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎
 1005.400 [0]  |
 1005.700 [0]  |
 1006.000 [3]  |∎∎∎∎∎

Latency distribution:
 10 % in 1.00 s 
 25 % in 1.00 s 
 50 % in 1.00 s 
 75 % in 1.00 s 
 90 % in 1.00 s 
 95 % in 1.01 s 
 99 % in 1.01 s 

Status code distribution:
 [success]   40 responses   
 [failed]    0 responses