benchmark: add benchmain/main.go to run benchmark with flag set

[ZhouyihaiDing]

1. Add a file benchmain/main.go to run the benchmark using go run main.go -flag=xxx.

In benchmark17_test.go, it uses "b *testing.B" to calculate the allocations, and b.N to stop benchmarks. In main.go, it uses ReadMemStats and do the calculation by it's own and timeout to stop benchmarks.

An example of main.go is
go run benchmark/benchmain/main.go -kbps=0 -mtu=0 -maxConcurrentCalls=1 -reqSizeBytes=1,1048576 -reqspSizeBytes=1,1048576 -runUnary=true -runStream=true -traceMode=true -latency=0s,5ms -timeout=10s
Flags include

-runUnary                        =bool
-runStream                       =bool
-traceMode                       =bool
-compressionMode                 =bool
-readLatency                     =slice of time.Duration like 0s,10ms
-readKbps                        =slice of int like 0,128,512
-readMtu                         =slice of int
-readMaxConcurrentCalls          =slice of int
-readReqSizeBytes                =slice of int
-readReqspSizeBytes              =slice of int
-timeout                         =time.Duration like 10s

runUnary and runStream can be set both. traceMode and compressionMode are false by default.
All flags have default settings.

2. Add profile flags

-cpuProfile       = string of filename
-memProfile       = string of filename
-memProfileRate   = int

when cpuProfile or memProfile is set, it will save the profile result into the file.

[dfawley]

Please resolve the conflicts and let us know when this is ready to review again. Sorry, thanks.

[MakMukhi]

Looks good, minor suggestions

[MakMukhi]

Why is pos needed?

[ZhouyihaiDing]

In the runStream, it need the position to indicate which steam is using.
Since runUnary and runStream shares the same function runBenchmark, runUnary set a postion without using it.

[MakMukhi]

Should we have only one variable traceMode with default value to be false?

[ZhouyihaiDing]

Done. I do the same with runCompressionMode. false by default, true if set.

[MakMukhi]

Should we change the name of this function since it isn't really reading from an intSlice?

[ZhouyihaiDing]

Done. I don't know which name is better, so I change it from IntSlice to Input.
Ready for review.

[MakMukhi]

nit: This could have have been an unnamed variable since this is not used in the function and is there only to maintain function signature.

return func(_ int) {
...
}

[dfawley]

If all your parameters are unnamed, you can do this instead:

return func(int) {
...
}