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: I68735b995fe1bce23edb8c092f2199fdde137acd

meta/main.yml

@@ -27,16 +27,14 @@ galaxy_info:
   platforms:
   - name: Debian
     versions:
-    - stretch
+    - buster
   - name: Ubuntu
     versions:
-    - bionic
+      - bionic
+      - focal
   - name: EL
     versions:
-    - 7
-  - name: opensuse
-    versions:
-    - 15
+    - 8
   galaxy_tags:
     - cloud
     - openstack

vars/suse.yml

@@ -1,19 +0,0 @@
----
-# Copyright 2017, SUSE Linux GmbH
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-tacker_distro_packages:
-  - rsync
-  - git-core
-  - systemd-devel