AbstractVerticle#stop / AbstractVerticle#start not executed via async

[Jotschi]

The AbstractVerticle#stop / AbstractVerticle#start methods are currently not being wrapped via Async#async.

The DeploymentManager invokes the methods using the context of the verticle (via runOnContext).

The context is provided via vertx.createWorkerContext / vertx.createEventLoopContext.

Options:

• Patch createWorkerContext / createEventLoopContext methods in Vert.x (e.g. by providing a custom thread factory.)
• Patch DeploymentManager to wrap the start / stop calls with Async.async
• Leave the behaviour unchanged. Thus it would be required for a user to manually use Async.async within the start method implementation of the custom verticle.
• Patch ContextImpl#runOnContext to use Async.async.
• Add startAsync / stopAsync abstract methods to io.vertx.loom.core.AbstractVerticle and invoke those from regular start / stop.