Add ability to define additional entries to be added the hostfiles

[seiji-thirdbridge]

trafficstars

I needed to be able to manage additional hostfile entries when running a multi-machine vagrantfile that contained both virtualbox and docker containers (managed by docker-compose).

[AntonioMeireles]

@seth-reeser

Hi! any reason for not merging this in ? IMHO it's a very worthy feature to provide ...

best regards

[planetchili]

Why isn't this merged?

[pedde07]

This would be very helpful for my usecase too.