refactor: Use vars/RedHat_N.yml symlink for CentOS, Rocky, Alma wherever possible

[richm]

We have a lot of requests to support Rocky and Alma in various system roles. The first part of adding support is adding vars/ files for these platforms. In almost every case, for a given major version N, the vars file RedHat_N.yml can be used for CentOS, Rocky, and Alma. Rather than making a copy of the RedHat_N.yml file, just use a symlink to reduce size and maintenance burden, and standardize this across all system roles for consistency.

NOTE: OracleLinux is not a strict clone, so we are not going to do this for OracleLinux at this time. Support for OracleLinux will need to be done in separate PRs. For more information, see https://github.com/linux-system-roles/cockpit/issues/130

Note that there may be more work to be done to the role to fully support Rocky and Alma. Many roles have conditionals like this:

some_var: "{{ 'some value' if ansible_distribution in ['CentOS', 'RedHat'] else 'other value' }}"
another_var: "{{ 'some value' if ansible_distribution in ['CentOS', 'Fedora', 'RedHat'] else 'other value' }}"

...

- name: Do something
  when: ansible_distribution in ['CentOS', 'RedHat']
  ...
- name: Do something else
  when: ansible_distribution in ['CentOS', 'Fedora', 'RedHat']
  ...

Adding Rocky and AlmaLinux to these conditionals will have to be done separately. In order to simplify the task, some new variables are being introduced:

__$rolename_rh_distros:
  - AlmaLinux
  - CentOS
  - RedHat
  - Rocky

__$rolename_rh_distros_fedora: "{{ __$rolename_rh_distros + ['Fedora'] }}"

__$rolename_is_redhat_distro: "{{ ansible_distribution in __$rolename_rh_distros }}"
__$rolename_is_redhat_distro_fedora: "{{ ansible_distribution in __$rolename_rh_distros_fedora }}"

Then the conditionals can be rewritten as:

some_var: "{{ 'some value' if __$rolename_is_redhat_distro else 'other value' }}"
another_var: "{{ 'some value' if __$rolename_is_redhat_distro_fedora else 'other value' }}"

...

- name: Do something
  when: __$rolename_is_redhat_distro | bool
  ...
- name: Do something else
  when: __$rolename_is_redhat_distro_fedora | bool
  ...

For tests - tests that use such conditionals will need to use vars_files or include_vars to load the variables that are defined in tests/vars/redhat_clone_vars.yml:

vars_files:
  - vars/redhat_clone_vars.yml

We don't currently have CI testing for Rocky or Alma, so someone wanting to run tests on those platforms would need to change the test code to use these.

[richm]

Also includes some improvements for updating existing PRs - update commit msg, PR title and body

[spetrosi]

I believe we remove symlinks when building RPM. We should ensure to keep symlinks that we add in this PR, and downstream I guess it doesn't matter to remove or keep much.

[richm]

I believe we remove symlinks when building RPM. We should ensure to keep symlinks that we add in this PR, and downstream I guess it doesn't matter to remove or keep much.

ok - but I think it already works - some roles have been using symlinks like this for years - which is what gave me the idea to just do this for all roles

[richm]

@spetrosi this is ready for review - you can also check one of the role PRs like https://github.com/linux-system-roles/nbde_client/pull/181