net/http: TestServerTimeouts flake

[bradfitz]

https://storage.googleapis.com/go-build-log/00bd9228/linux-amd64-race_7b9a8856.log

2016/11/23 21:53:28 http: TLS handshake error from 127.0.0.1:41658: read tcp 127.0.0.1:34022->127.0.0.1:41658: use of closed network connection
--- FAIL: TestServerTimeouts (0.79s)
	serve_test.go:512: http Get #2: Get http://127.0.0.1:38239: http: server closed idle connection
FAIL
FAIL	net/http	11.248s

[gopherbot]

CL https://golang.org/cl/34490 mentions this issue.