Configure allowable status codes for HTTPFuture and HTTPSFuture

Summary: Expose new setExpectStatus() method on BaseHTTPFuture. If set, any status code not in the array will trigger an error state in HTTPFutureResponseStatusHTTP.

Test Plan: Used HTTPSFuture with resolvex() and tested against various status codes.

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, aran

Differential Revision: https://secure.phabricator.com/D6899