Azure: Make it possible to configure distro-specific stuff
    
    This allows to run IPA tests on Azure using any distro.
    
    To achieve this, one has to do:
    1) place a platform specific template on 'ipatests/azure/templates/'
    and make a soft link from 'ipatests/azure/templates/variables.yml' to
    the new template.
    2) place a configuration templates on these paths
    3) templates have to answer the questions such as:
      a) which Docker image to use to build IPA packages (rpm, deb, etc.)
      b) how to prepare Build environment
      c) how to build IPA packages
      d) how to prepare environment to run Tox tests
      e) how to prepare environment to run WebUI unittests
      f) which base Docker image to use to build the new image to run
         IPA tests within it
    
    Fixes: https://pagure.io/freeipa/issue/8202
    Signed-off-by: Stanislav Levin <slev@altlinux.org>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>