After futurist calls were introduced, the code became difficult to
understand. For example, local variables are used something like global.
To keep the code easier to understand, the usage of local variables
should be more scoped.
This commit introduces a wrapper function for futurist.ThreadPoolExecutor
and converts inline functions into normal methods.
I believe it improves the code readability a lot.
Change-Id: Id5b7a06c50e397c8c27447322d7f64f2d65c06b6
56ae087995