It would be good to have Dockerfiles for multiple Fedora versions, and
possibly even other operating systems like Red Hat Enterprise Linux or
CentOS, so that people can use the toolbox on different host OSes.
In the future, it would be nice to have multiple toolbox containers
corresponding to different OSes exist side by side. One could then
have a Fedora 29 environment on a Fedora 28 host and so on.
