fbcode_builder: getdeps: use testpilot when available to record tests
fbcode_builder: getdeps: use testpilot when available to record tests

Summary:
If `testpilot` is available, generate a buck compatible json file describing the available test binaries and feed that to testpilot to have it run the tests.

A later (yet to be written) diff will be able to pass appropriate flags down to testpilot in continuous runs and that will allow testpilot to auto-disable and file tasks for tests in the opensource builds.

Reviewed By: simpkins

Differential Revision: D14766856

fbshipit-source-id: 4e144ff18f6788cf5e830d29788eabd2dbbae46a

nodakai/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,wez/watchman,nodakai/watchman,nodakai/watchman,wez/watchman,wez/watchman,wez/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,facebook/watchman,wez/watchman,wez/watchman,wez/watchman,wez/watchman,wez/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,facebook/watchman