We have a *ton* of stuff in devstack that is very linear, specifically
the ten-ish minutes we spend loading osc to run a single API command
against something. We also generate configs, sync databases, and other
things that use one core of our worker and make our runtime longer
than it really needs to be.
The idea in this patch is to make it super simple to run some things
in the background and then wait for them to finish before proceeding
to something that will require them to be done. This avoids the
interleaving you would expect by redirecting the async tasks to a log
file, and then cat'ing that log file synchronously during the wait
operation. The per-task log file remains so it's easier to examine
it in isolation.
Multiple people have reported between 22-30% improvement in the
time it takes to stack with this. More can be done, but what is here
already makes a significant difference.
Change-Id: I270a910b531641b023c13f75dfedca057a1f1031
30d9bf9a6d