[utils] build_graphs: add "function" to function declaration
[utils] build_graphs: wrap some code segments into functions

And also rename camelCase() function into underscore_function()
because I already start write functions in underscore_function() in
bash.
[utils] build_graphs: run benchmark multiple times and count average.

By default 5 times.
[utils] build_graphs: make number of random iterations configurable
[utils] build_graphs: make clients string configurable