OSS release tests currently run with hardcoded Python 3.7 base. In the future we will want to run tests on different python versions.
This PR adds support for a new `python` field in the test configuration. The python field will determine both the base image used in the Buildkite runner docker container (for Ray client compatibility) and the base image for the Anyscale cluster environments.
Note that in Buildkite, we will still only wait for the python 3.7 base image before kicking off tests. That is acceptable, as we can assume that most wheels finish in a similar time, so even if we wait for the 3.7 image and kick off a 3.8 test, that runner will wait maybe for 5-10 more minutes.
Currently nightly tests are unable to finish in a day because of concurrency group limit on `large` tests. This is an attempt to adjust the limits so buildkite can run / finish more tests. I will observe which tests fall into the `enormous` group and adjust the test resource / concurrency group limits again.
E.g. long running tests run on small clusters (often 8 CPUs) but block other jobs for a long time. We should thus add more granularity to the concurrency groups.
Additionally, limits have been slightly adjusted to make more sense (e.g. 8 GPUs are now small-gpu, 9+ GPUs large-gpu, instead of 7 for small-gpu and 8 for large-gpu).
This PR reduces the concurrency limit. Based on the back of envelope calculation, the current concurrency limit can easily exceed the service quota.
Given large == 2048 vCPUs, it will use about 20K vCPUs, which is slightly larger than the limit.
This PR adds concurrency groups to Buildkite release test runs with new release test package. Five concurrency groups are defined (large-gpu, small-gpu, large, medium, small). If not specified manually, concurrency groups are inferred from used cluster resources.
Example pipeline: https://buildkite.com/ray-project/release-tests-branch/builds/55#09109eac-d22e-43bc-889e-078cfb037373 (click on Artifacts --> pipeline.json)
