Fix http_server_early_client_close_test.

Fix http_server_early_client_close_test.

A too early close of the HttpServer was responsible for an uncought
socket error. We now wait with HttpServer close to we

1) Have sent all data to the server.
2) The server are done receiving all data for the potential request.

BUG=http://code.google.com/p/dart/issues/detail?id=10408

Committed: https://code.google.com/p/dart/source/detail?r=23196

[Anders Johnsen, 2013-05-25 20:22:40]

TBR

[Anders Johnsen, 2013-05-26 05:29:53]

Committed patchset #1 manually as r23196 (presubmit successful).

[Søren Gjesse, 2013-05-27 06:27:48]

lgtm