Fix deprecated -dns argument. Add host support

.kitchen.yml example:
```
driver:
  name: docker
  use_sudo: false
  add_host:
    myfakehost1.local: 127.0.0.1
    myfakehost2.local: 127.0.0.2
```
If you wanted, you could always add a docker version check, for example:

```
if version_above?('1.2.0') 
  Array(config[:dns]).each {|dns| cmd << " --dns #{dns}"}
else 
  Array(config[:dns]).each {|dns| cmd << " -dns #{dns}"}
end 
```