Maintaining Fedora-Dockerfiles

[Lalatendu Mohanty]

I was looking at the Fedora-Dockerfiles git repo and realised that in 
current state it is difficult to maintain the dockerfiles for 3 versions 
of Fedora i.e. F21, F22 and Rawhide.

One of the issue is the change from yum to dnf (dnf does not work in 
F20) in the dockerfiles. Though F20 is not in the supported versions, 
but  this is a classic example of difference between versions of Fedora.

To handle this issue I will suggest to have different branches for each 
releases and keeping the master for rawhide. After every Fedora release 
we can create branch from master for that release and keep the master 
branch for rawhide.

However I understand this is more work for us, but IMO we need to follow 
this or something for easy maintenance of the files.

[1] https://github.com/fedora-cloud/Fedora-Dockerfiles.git

Thanks,
Lala