Fixed test jetty handler writing 1-too-many bytes to http response

Response output stream throws IOException when number of bytes written
exceeds set response content length. Depending on operating system
scheduller, the exception may be handled before content is fully written
to network socket, which in turn results in IOException and failure
in GetResumeTest. The test failure was observed on relatively slow
linux box, where 1 in ~10 builds failed before this change.

Signed-off-by: Igor Fedorenko <igor@ifedorenko.com>