Remove references to unsupported operating systems

All references to Gentoo, SUSE, Debian stretch and Centos-7  are removed.
Conditional tasks, ternary operators and variables are simplified where possible
OS specific variables files are generalised where possible

Change-Id: I214f35cfff5fa9dd703733f795d6a7e414d729ca

meta/main.yml

@@ -22,17 +22,14 @@ galaxy_info:
   platforms:
     - name: Debian
       versions:
-        - stretch
+        - buster
     - name: Ubuntu
       versions:
-        - xenial
         - bionic
+        - focal
     - name: EL
       versions:
-        - 7
-    - name: opensuse
-      versions:
-        - 15
+        - 8
   categories:
     - systemd
     - development

tasks/main.yml

@@ -36,7 +36,6 @@
   with_items: "{{ systemd_networkd_package_repos_keys | selectattr('keyfile','defined') | list }}"
   when:
     - ansible_facts['os_family'] | lower == 'redhat'
-    - ansible_facts['distribution_major_version'] is version('8', '>=')
 
 - name: Ensure GPG keys have the correct SELinux contexts applied
   command: restorecon -Rv /etc/pki/rpm-gpg/
@@ -44,7 +43,6 @@
   changed_when: false
   when:
     - ansible_facts['os_family'] | lower == 'redhat'
-    - ansible_facts['distribution_major_version'] is version('8', '>=')
 
 # Handle gpg keys manually
 - name: Install gpg keys
@@ -61,7 +59,6 @@
   delay: 2
   when:
     - ansible_facts['os_family'] | lower == 'redhat'
-    - ansible_facts['distribution_major_version'] is version('8', '>=')
 
 # NOTE(jrosser) this repo is configured with the path to the first gpg key provided
 - name: Install the EPEL repository
@@ -76,7 +73,6 @@
     includepkgs: 'systemd-networkd'
   when:
     - ansible_facts['os_family'] | lower == 'redhat'
-    - ansible_facts['distribution_major_version'] is version('8', '>=')
   register: install_epel_repo
   until: install_epel_repo  is success
   retries: 5