Added new "fast" Showcase build flavor
Added new "fast" Showcase build flavor

Reviewed By: passy

Differential Revision: D33583667

fbshipit-source-id: 910b1d4812d3d68f339e27e1a028e87ef1d2c595

facebook/fresco,facebook/fresco,facebook/fresco,facebook/fresco,facebook/fresco,facebook/fresco