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: I3781543c5f5005d578a4010ac8ff41dbdcc8407a

meta/main.yml

@@ -25,13 +25,11 @@ galaxy_info:
   platforms:
   - name: Debian
     versions:
-    - stretch
+      - buster
   - name: Ubuntu
     versions:
-    - xenial
-  - name: opensuse
-    versions:
-    - 15
+      - bionic
+      - focal
   galaxy_tags:
     - cloud
     - python

vars/suse.yml

@@ -1,24 +0,0 @@
----
-# Copyright 2018, taseer94@gmail.com
-# All rights reserved.
-#
-# 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.
-
-cache_timeout: 600
-
-blazar_distro_packages:
-  - git-core
-  - libxml2
-
-blazar_devel_distro_packages:
-  - libxml2-devel