Add an error type if parsing the response failed

Summary: An error type for parsing response failure.

Test Plan: Unit tests

Reviewed By: fma@fb.com

Subscribers: trunkagent, hannesr, bmatheny, seanc

FB internal diff: D1737871

Signature: t1:1737871:1418655476:b7e52ba7ee9231f3002b928b7f713504ac7beb96
Bump version to 8:0