upstream CI: Use Azure 'loops' to create stages

This patch modify the pipelines to create stages using the 'each'
expression on Azure pipelines, so that the configuration and the list of
distributions can be set using variables.

Testing CentOS 8 Stream and Galaxy collections still need to be handled
in a separate group, although, the pipeline configuration becomes easily
changed, specially when updating Ansible versions.

infra/azure/templates/build_container.yml

@@ -1,7 +1,5 @@
 ---
 parameters:
-  - name: job_name_suffix
-    type: string
   - name: distro
     type: string
   - name: python_version
@@ -11,7 +9,7 @@ parameters:
     default: ""
 
 jobs:
-- job: BuildTestImage${{ parameters.job_name_suffix }}
+- job: BuildTestImage_${{ join('_', split(parameters.distro, '-')) }}
   displayName: Build ${{ parameters.distro }} test container
   steps:
   - task: UsePythonVersion@0