Support centos 8

[emiliogq]

Maybe have another Dockerfile to set the base image to centos 8 or just change the current one

[dneise]

I tried it locally on my machine with Centos 8 recently .. it did not work right away.
I think a few packages which exist for Centos 7 .. do not exist for Centos 8 anymore .. or were renamed.

[dneise]

Generally I think it would be easiest for us, if we only provide this image for one single Centos version. I personally would simply only support the newest (i.e. Centos 8?).
Of course this does not solve all problems for all people in the world. But I guess for the majority.