Switch to queue based measurer

[jonathanmetzman]

This issue tracks switching to the queue based measurer. This will make measuring horizontally scalable, making experiments shorter, cheaper and results more realtime. It is also necessary for the new architecture we are switching to. This is essentially the second time I am trying to do this. The first time I did it on a second branch called queue. queue was pretty much ready to merge in #570. But #570 is basically impossible to land now because we completely changed measuring thanks to clang coverage. Instead of trying this same failed approach again, I am going to merge in pieces of #570 incrementally, before switching over to the queue system.