Fix up 2to3 complaints. I've decided to do with wrapping list
comprehension inside list() to get the generators to run in several
places instead of list(map( or list(filter( which seem less readable to
me.
pylorax users will need to change to using dnf and pass a dnf.Base()
object as the dbo argument instead of a yum object as the yum or ybo
argument. See the lorax script for an example of how to do this.
The lorax cmdline argument --excludepkgs has been removed since dnf
doesn't appear to have any way to support it and packages should be
controlled using templates anyway.