[BUG] OS compatibility listing CentOS, but hardcoded 'dnf' in commands

[iranzo]

What happened:

Documentation states:

Fedora 33/34
CentOS 8 Stream
RHEL 8
CentOS 7
Ubuntu 20.04

What you expected to happen:

Support for CentOS7

How to reproduce it (as minimally and precisely as possible):

1. try to launch the installer script
2. it complains about missing dnf (as yum is the default in centos7)

Anything else we need to know?:

Environment:

CentOS Linux release 7.7.1908 (Core)

Relevant Logs

[iranzo]

/kind docs

[iranzo]

Problem in bash script seems to come from hardcoding the OS as 'CentOS_8_Stream' and then downloading wrong repofiles, leading to a failure in yum install.

Seems, that even after fixing repo for CentOS7, cri-o fails to install because of broken dependencies

[iranzo]

[cooktheryan]

/assign cooktheryan

[oglok]

I don't think we want to support Centos 7.

[cooktheryan]

@oglok I could +1 removing Centos 7.

Looking for a final +1 from @rootfs or @fzdarsky

[cooktheryan]

Going to run the AIO and see if the issue still occurs. Currently when installing the containers common package issue with RPM install.

[alknopfler]

possible fix here: #415