mcreplay: Include service name and source region in asynclog spooled event
mcreplay: Include service name and source region in asynclog spooled event

Summary:
Adds service name and source region into asynclog spooled event. This is helpful for
logging, debugging, filtering.

Reviewed By: kkondaka

Differential Revision: D25350403

fbshipit-source-id: 5c902d9bd818a0a42c75402d2dddfcca4dcf645e

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