Get MassTransit running on .net core.

Some related dependencies (there are a lot more that deserve tracking down):

• TopShelf has a related issue, here: Topshelf/issues/277
• RabbitMQ's rabbitmq-dotnet-client has a related issue, here: rabbitmq-dotnet-client/issues/148.
• NewId has a related issue, here: NewId/issues/3