Add a test for websocket hibernate + timeout and fix this use case

The issue was that we were calling erlang:hibernate before a
receive .. after .. end call. Erlang hibernates the process before
reaching the receive instruction and we therefore couldn't enter
the after clause when hibernating.

This is now fixed by using erlang:send_after instead and receiving
that message instead of using an after clause.

test/ws_timeout_hibernate_handler.erl

@@ -0,0 +1,29 @@
+%% Feel free to use, reuse and abuse the code in this file.
+
+-module(ws_timeout_hibernate_handler).
+-behaviour(cowboy_http_handler).
+-behaviour(cowboy_http_websocket_handler).
+-export([init/3, handle/2, terminate/2]).
+-export([websocket_init/3, websocket_handle/3,
+	websocket_info/3, websocket_terminate/3]).
+
+init(_Any, _Req, _Opts) ->
+	{upgrade, protocol, cowboy_http_websocket}.
+
+handle(_Req, _State) ->
+	exit(badarg).
+
+terminate(_Req, _State) ->
+	exit(badarg).
+
+websocket_init(_TransportName, Req, _Opts) ->
+	{ok, Req, undefined, 1000, hibernate}.
+
+websocket_handle(_Frame, Req, State) ->
+	{ok, Req, State, hibernate}.
+
+websocket_info(_Info, Req, State) ->
+	{ok, Req, State, hibernate}.
+
+websocket_terminate(_Reason, _Req, _State) ->
+	ok.