Limit the parallelism of user Chromium builds to 8 using an alias

[phistuck]

But temporarily remove the alias before building the image itself.

[phistuck]

If I understand the concept correctly, I feel like host-level affinity limits would be too limiting for the situations where someone needs a bit more power for a short while and the load is very low, but maybe I am just paranoid.

[ishitatsuyuki]

@phistuck The affinity limits is considered to affect the performance very minimally: I only plan to shut down the hyperthreads, which at most affects ~15% performance.

This looks fine though. Let's add a note so we don't forget to revert this once we have affinity implementation.

[phistuck]

I guess I forgot to mention I added the requested comment?