This patch set uses concurrent.futures.ThreadPoolExecutor
[0] to retrieve multiple Barbican secrets concurrently.
This is because currently it is only possible to retrieve
1 secret payload from Barbican at a time -- for revisions
with several dozen secrets it is therefore too costly
to serially perform these API requests.
A new configuration option is added to the [barbican]
group called `max_workers` which specifies the number
of threads to use. The default value is 10. Note that:
"If max_workers is None or not given, it will default
to the number of processors on the machine, multiplied by 5"
[0] so the default is 10 for 2 * 5 which is overly
conservative if anything.
If any error occurs during any of the requests a 500
is raised with appropriate details.
[0] https://docs.python.org/3/library/concurrent.futures.html#concurrent.futures.ThreadPoolExecutor
Change-Id: I76a5bb6c345054e160c14bdf9fb7087e3a746a5e
d27ab2d8ea