Remove magic numbers from benchmark utils

There are many hardcoded values for sleep, timeout and poll interval in
benchmark.*.utils. This patch adds oslo config options for all of them.

Change-Id: I7ddf6244ab87e748bb2daf6502db56df13034168
Trello: https://trello.com/c/aIcMrSPM
Merge "Remove magic numbers from benchmark utils"