[Feature Request] Add a NoneTransport for event processing case.

#### Describe the feature

Currently, there are three `Transport` implements in vert.x, and for my use case, I am only using vert.x as an event processing framework to leverage its thread safety in vertical and the event bus, any networking is handled by an internal RPC framework.

So How about adding an option to `VertxBuilder` eg, `enableTransport(false)`?

#### Use cases

Use Vertx for async event processing only.

#### Contribution

I would like to contribute if this feature is acceptable.