This replaces the 'run-tests-deps' make target with a python function that will directly
read moz.build files, emit them with TestManifestEmitter, then consume them with
TestManifestBackend. Because the TestResolver is the only place that actually reads the
test metadata files, we can remove this logic from the CommonBackend as well.
MozReview-Commit-ID: DXgMoeH5dKf
MozReview-Commit-ID: HstZ57qkqf2
--HG--
extra : rebase_source : f377fa6863ef66d3adb86ed64f844e346686862f
Andrew Halberstadt