[buck2] Update hardcoded buck-out constants to use buck2 paths
[buck2] Update hardcoded buck-out constants to use buck2 paths

Summary: Changelog: [internal]

Reviewed By: mroch

Differential Revision: D38134493

fbshipit-source-id: a7697d0bc8dceeba11bba1270ef8c148630c2b98

mroch/flow,facebook/flow,facebook/flow,mroch/flow,mroch/flow,facebook/flow,facebook/flow,facebook/flow,mroch/flow,mroch/flow,mroch/flow,facebook/flow,mroch/flow,facebook/flow