Re-enable WebSocketSpec test

In commit 115f79c38fa28570baa9c57190668e9d18d9ab59 I disabled a test that was causing intermittent failures. Need to re-enable the test and fix the underlying failure.

See also #2646.

https://playframework2.ci.cloudbees.com/job/play2-PRs/2083/consoleFull

```
[info] WebSocketSpec
[info] 
[info] Plays WebSockets should
[info] + allow consuming messages
[info] + allow sending messages
[info] + close when the consumer is done
[info] + clean up when closed
[info] + allow rejecting a websocket with a result
[info] 
[info]   allow handling a WebSocket with an actor
[info]   + allow consuming messages
[info]   + allow sending messages
[info]   + close when the consumer is done
[info]   + clean up when closed
[info]   + allow rejecting a websocket with a result
[info]   + aggregate text frames
[info]   + aggregate binary frames
[info]   + close the websocket when the buffer limit is exceeded
[info]   ! close the websocket when the wrong type of frame is received
[error]      IOException: : Connection reset by peer  (FileDispatcher.java:-2)
[error] sun.nio.ch.FileDispatcher.read0(Native Method)
[error] sun.nio.ch.SocketDispatcher.read(SocketDispatcher.java:21)
[error] sun.nio.ch.IOUtil.readIntoNativeBuffer(IOUtil.java:202)
[error] sun.nio.ch.IOUtil.read(IOUtil.java:169)
[error] sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:243)
[error] org.jboss.netty.channel.socket.nio.NioWorker.read(NioWorker.java:64)
[error] org.jboss.netty.channel.socket.nio.AbstractNioWorker.process(AbstractNioWorker.java:108)
[error] org.jboss.netty.channel.socket.nio.AbstractNioSelector.run(AbstractNioSelector.java:318)
[error] org.jboss.netty.channel.socket.nio.AbstractNioWorker.run(AbstractNioWorker.java:89)
[error] org.jboss.netty.channel.socket.nio.NioWorker.run(NioWorker.java:178)
```