Allow HttpClient to remember my cookie

When the target host sets a cookie, the Httpclient should remember it. That way in the module I won't have to manually extract it, and then put it in the next request.

If some for reason the module decides to send to different hosts, the HttpClient mixin should know which one to use. Also, as you can see only send_request_cgi() uses this feature, I don't think send_request_raw should be using it because it's supposed to be the most basic form of send_request_*.

For testing, use test/modules/auxiliary/test/cookie_test.rb, and then you'll have to use wireshark to verify it's working properly. You can set the rhost to 208.118.237.137 if you want, that's metasploit.com.

[SeeRM #8706]