- Add possibility to remove prereq. packages installation BEFORE
     * Crucial logic violation - if we don't have any repo\
       have them configured in wrong way - stage will always fail.
     * install prereq. packages after all - sounds stupid, but correct.
     * By default - it will still try to install prereq. We don't want to
       broke OLD logic.See readme, how-to overide such behaviour.
   - don't update cache per-repo - it's simply useless and may fail due p1.
     Run update only once - after all repos configured\reconfigured
   - Add new option at system:refresh_repos_meta - for case, when update
     should not be run in any case. By default - true.
   - remove 99proxies-salt-{{ name }} along with disabled repo
   - fix duplicate 'clean_file' option

Closes-Bug: PROD-15992 (PROD:15992)

Change-Id: I4b312f82f65be80e7726f62482978f68c25746a3