Incorrect Docker URL for RedHat

[Aaron Hicks]

When using Kolla-Ansible with RedHat it incorrectly uses a Docker repository URL based on the distribution name `redhat` when the Docker site used `rhel`.

https://github.com/openstack/kolla-ansible/blob/master/ansible/roles/baremetal/defaults/main.yml#L13

This sets the base URL to: https://download.docker.com/linux/redhat
The correct base URL should be: https://download.docker.com/linux/rhel

This results in the error:

```
TASK [baremetal : Install docker rpm gpg key] ****************************************************************************************
fatal: [hpcwseed01.hpcf.nesi.org.nz]: FAILED! => {"changed": false, "msg": "failed to fetch key at https://download.docker.com/linux/redhat/gpg , error was: HTTP Error 404: Not Found"}
```

[Aaron Hicks (aethylred)]

Workaround is to specify the docker URL as a host/group/extra variable:

```
docker_yum_url: "https://download.docker.com/linux/rhel"

```

[Aaron Hicks (aethylred)]

In addition, the broken repo file with the incorrect URL needs to be deleted, as it may cause dnf/yum to fail.

[Aaron Hicks (aethylred)]

I think a better correct setting is:

```
docker_yum_url: "https://download.docker.com/linux/{{ 'centos' if ansible_facts.distribution | lower == 'redhat' else ansible_facts.distribution | lower }}"
```

However, this may not be suitable for release. Also, the podman and buildah packages have to be removed.