RemoteCacheManager can block waiting to connect/ping

When running Java Hot Rod client on top sensitive environments to blocking, e.g. Vert.x, you realise that the RemoteCacheManager constructor blocks.

This is due to the fact that RCM constructor waits to establish connections with the initial servers and sends pings on startup.

You can avoid RCM doing this by passing start=false as parameter and then calling start() manually, but start() is a blocking method.

So, we should have an alternative start() method that returns a CompletableFuture, hence avoiding any blocking.