Log request exptime to Mcrouter Request Scuba
Log request exptime to Mcrouter Request Scuba

Summary: As titled.

Reviewed By: stuclar

Differential Revision: D37811452

fbshipit-source-id: 5d79a5f5646eec863d32f7a58fcad03c45538a12

facebook/mcrouter,facebook/mcrouter,facebook/mcrouter,facebook/mcrouter