test: fix hanging http obstext test

Set the Connection header to 'close' to work around a v0.10 quirk.
Prevents the test from timing out due to a still open TCP connection.
Test introduced in 1e45a611 ("deps: update http-parser to version 1.2").

PR-URL: https://github.com/nodejs/node/pull/5511


Reviewed-By: James M Snell <jasnell@gmail.com>