Remove ChannelHandler.beforeAdd(...) and beforeRemove(...) method
Correctly handle SslHandler.handshake() and tests
Rename SslHandler.handshake() to handshakeFuture() which will just return a Future<Channel> that will notified once the handshake completes.

This also means there is no way to trigger a handshake manually because netty will just do it for you when either:
 * The channel becomes active
 * Or the SslHandler is added and the channel is active already
Add test for concurrent add /remove
Minimize the sleep time
Disable test as this will be fixed by another pull-req
Make addAfter called async