This clears up some confusion and undocumented behavior around platforms in
source-tests (and available to any job).
With this change, the attributes come out like this:
"source-test-mozbase-linux64/opt": {
"attributes": {
"build_platform": "linux64",
"build_type": "opt",
"kind": "source-test",
"run_on_projects": [
"integration",
"release"
]
},
MozReview-Commit-ID: HN1Zi8YUf0