rkt: Support host and none dns options
rkt: Support host and none dns options

Fixes #2025

frundh/nomad,frundh/nomad,achanda/nomad,barnardb/nomad,novilabs/nomad,barnardb/nomad,kmalec/nomad,frundh/nomad,dvusboy/nomad,barnardb/nomad,burdandrei/nomad,kmalec/nomad,Ashald/nomad,hashicorp/nomad,barnardb/nomad,hooklift/nomad,nak3/nomad,kmalec/nomad,nak3/nomad,achanda/nomad,dvusboy/nomad,hashicorp/nomad,burdandrei/nomad,dvusboy/nomad,barnardb/nomad,kmalec/nomad,barnardb/nomad,barnardb/nomad,burdandrei/nomad,dvusboy/nomad,Ashald/nomad,dvusboy/nomad,novilabs/nomad,burdandrei/nomad,achanda/nomad,nak3/nomad,Ashald/nomad,hooklift/nomad,Ashald/nomad,hooklift/nomad,hooklift/nomad,nak3/nomad,diptanu/nomad,nak3/nomad,Ashald/nomad,nak3/nomad,novilabs/nomad,kmalec/nomad,novilabs/nomad,frundh/nomad,frundh/nomad,achanda/nomad,diptanu/nomad,diptanu/nomad,Ashald/nomad,frundh/nomad,burdandrei/nomad,novilabs/nomad,burdandrei/nomad,nak3/nomad,hooklift/nomad,hooklift/nomad,novilabs/nomad,hashicorp/nomad,dvusboy/nomad,kmalec/nomad,burdandrei/nomad,achanda/nomad,kmalec/nomad,diptanu/nomad,frundh/nomad,hashicorp/nomad,diptanu/nomad,novilabs/nomad,achanda/nomad,achanda/nomad,diptanu/nomad,hooklift/nomad,Ashald/nomad,diptanu/nomad,hashicorp/nomad,dvusboy/nomad,hashicorp/nomad