Reduce flakiness of OkHttp tests

Copy of the test changes from a pending upstream
pull-request:
https://github.com/square/okhttp/pull/1348

----

Android has been receiving reports of some tests being flaky
on what are probably lower-spec devices.

This introduces delays into tests where sockets are being
poisoned after the entire response body has been written to
them *and* where there are follow-up requests.

Bug: 18953235
Change-Id: Ic2d281a3faad6082819ef6d57b3489bcd6dbd474
(cherry picked from commit 75a7afac)