RFR [13] 8217976: test/jdk/java/net/httpclient/websocket/WebSocketProxyTest.java fails intermittently

[Chris Hegarty]

WebSocketProxyTest is a new test that was added recently. It fails once
in every few hundred runs. The test uses a preexisting test-only proxy
server. There is a race when closing the server; the close method
iterates over all connections while another thread may be adding a new
connection. The solution proposed here is to take a copy of the
connection list and iterate over it, rather than the connection list
itself.  ( I also did a little clean up and added some consistency to
proxy debug messages, since it was more difficult to reason about the
test's behavior from its log than it should have been )

http://cr.openjdk.java.net/~chegar/8217976/webrev.00/

-Chris.