Move buildbot step to yaml

[shinglyu]

This is a step of servo/saltfs#316

After this patch lands, we'll PR the saltfs code to read from this yaml file, and dynamically generate test steps at runtime.

cc @aneeshusa @edunham

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This change is

[wafflespeanut]

r? @larsbergstrom

[nox]

I'm confused. Since the YAML change, how does Buildbot know the difference between a compile step and a test step?

[aneeshusa]

@nox Heuristics, based on the command given to mach. (e.g. build-cef vs test-wpt).
One of the goals of switching to YAML was to decrease the complexity of changing build steps to make it easier to contribute to infra, so I used heuristics instead of hardcoding many things. This allows for a simple list of strings, instead of requiring each line to be a dictionary with type: Compile, etc. keys.

Also, Test and Compile steps have essentially the same behavior, so in practice the difference is moot. The most visible difference right now is what they're labeled on the Buildbot display, which should improve with servo/saltfs#337.

[aneeshusa]

Can you update this to include the changes from servo/saltfs#341?

[nox]

@aneeshusa AFAIK buildbot stops on a compile step failing to succeed, while it doesn't on a test step.

[aneeshusa]

@nox You're right, I completely overlooked that. Seems like I learn something new about Buildbot every day!

[shinglyu]

@aneeshusa I just force pushed a version with servo/saltfs#341

[aneeshusa]

@bors-servo r+

@shinglyu Thanks! Let me know if you have any questions while making the other PR.

[bors-servo]

📌 Commit c01aa9c has been approved by aneeshusa

[bors-servo]

💡 This pull request was already approved, no need to approve it again.

[bors-servo]

📌 Commit c01aa9c has been approved by aneeshusa

[bors-servo]

⌛ Testing commit c01aa9c with merge fbc5754...

[bors-servo]

☀️ Test successful - android, arm32, arm64, linux-dev, linux-rel, mac-dev-unit, mac-rel-css, mac-rel-wpt