don't pass --collection or --purpose to tpx in local runs
don't pass --collection or --purpose to tpx in local runs

Summary:
Fix local test runs. Previously, they were silently passing, because
they skipped tests that were unknown to tpx. Instead, treat local runs
separately from CI diff runs.

Reviewed By: xavierd

Differential Revision: D37287032

fbshipit-source-id: a3a88e117cd0e078e18c0f795bae467768d812a5

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift