Detect RHEL variants even if they are of type atomic.
Detect RHEL variants even if they are of type atomic.

If the nomenclature changes, we can update this, but in general atomic
boxes should start with atomic-<whatever>, so a rhel variant should be
atomic-rhel-<version>[-<variant>].

mairin/oh-my-vagrant,purpleidea/oh-my-vagrant,geekcheng/oh-my-vagrant,ncoghlan/oh-my-vagrant,mairin/oh-my-vagrant,goern/oh-my-vagrant,geekcheng/oh-my-vagrant,purpleidea/oh-my-vagrant,gpjonesii/oh-my-vagrant,mairin/oh-my-vagrant,LalatenduMohanty/oh-my-vagrant,goern/oh-my-vagrant,ncoghlan/oh-my-vagrant,bhalothia/oh-my-vagrant,br0ziliy/oh-my-vagrant,goern/oh-my-vagrant,bhalothia/oh-my-vagrant,gpjonesii/oh-my-vagrant,geekcheng/oh-my-vagrant,purpleidea/oh-my-vagrant,bhalothia/oh-my-vagrant,br0ziliy/oh-my-vagrant,LalatenduMohanty/oh-my-vagrant,LalatenduMohanty/oh-my-vagrant,br0ziliy/oh-my-vagrant,gpjonesii/oh-my-vagrant