Implement new test

But some tests fail

with atmosphere 2.2.0 and jetty 9.2.2.v20140723 (or 9.1.5.v20140505)
* server transport ws protocol close should close the socket
* server transport ws protocol close should detect the client's
disconnection

with atmosphere 2.1.7 and 2.0.9 and jetty 9.2.2.v20140723 (or
9.1.5.v20140505)
* server transport ws protocol close should close the socket

Not sure where the bug lies on atmosphere or jetty but because it fails
also with atmosphere 2.1.1, it seems that
https://github.com/Atmosphere/atmosphere/issues/1623 has nothing to do
with this issue.