Adding various fixes for CORS request/response handling

There are a few tests that verify that a SockJS server responds with
proper CORS HTTP response headers. Some of these test do not send
requests with the appropriate CORS request headers which could mean that
servers that follow the CORS specification [1] might fail the requests by
not sending back CORS repsonse headers

This PR attement to fix this issue.

[1] http://www.w3.org/TR/cors/#resource-requests '6.1 Simple Cross-Origin Request, Actual Request, and Redirects'
The reason for leaving out the test for no Origin is that the request being sent would no longer be a valid  [CORS request](http://www.w3.org/TR/cors/#resource-requests). A server implementation could simply let the request through as it might be a valid request for a resource.  
The issue I ran into was that we using a general CORS [handler](https://github.com/netty/netty/blob/master/codec-http/src/main/java/io/netty/handler/codec/http/cors/CorsHandler.java) which does not know anything about SockJS.