Rebalance CircleCI jobs?

[effigies]

There have been a few recent changes that have impacted CI runtimes:

1. We're no longer building Python 2 images
2. We're no longer running tests on Python 2
3. Docs have been separated from tests

Current CI jobs have the following runtimes:

• Docs: ~4min
• Tests: ~20min (~25 on master, due to saving Docker image)
• FSL reuse + SPM: ~35min
• SPM Nested + FSL FEEDS: ~44min
• SPM DARTEL: ~75min

DARTEL is extremely long-running, and there's nothing to be done, there. But otherwise, does it seem worth the effort to rebalance and get the other three test jobs closer to a consistent duration? The ideal would probably be 3x 30-35min jobs.

OTOH, if we're moving examples to niflows, will we still be running them here? If not, it's probably not worth the time.

[satra]

moving the examples to niflows and engaging the testing machinery there would be good a test in itself.

[effigies]

Okay. We'll just need to consider how to identify breakage in examples before releases.

[oesteban]

We haven't modified these workflows forever - what about caching the workflows as we are doing for parts of sMRIPrep and fMRIPrep, or even the "updatehash=True"? Do we really need to run DARTEL with every build?