ci: Add a script for generating CPU usage graphs This commit checks in a script which generates CPU usage graphs over time, expanding on the previous comment that was include in the collection file. Some example graphs from the [latest build](https://dev.azure.com/rust-lang/rust/_build/results?buildId=717) look like: ![dist-x86_64-apple](https://user-images.githubusercontent.com/64996/59520676-16c5b000-8e90-11e9-9188-27001911f270.png) ![x86_64-msvc-1](https://user-images.githubusercontent.com/64996/59520677-175e4680-8e90-11e9-8568-4b564807324e.png) ![x86_64-mingw-1](https://user-images.githubusercontent.com/64996/59520680-175e4680-8e90-11e9-939d-a73c7224582f.png) ![test-various](https://user-images.githubusercontent.com/64996/59520682-175e4680-8e90-11e9-9980-900ed4eeb8f4.png)