Add common.repositories pillar
    
    This adds a common/repositories/ pillar directory with repository
    definitions which can be included from other pillars as needed. For now,
    I added files for all repositories I could find in the pillar
    - in a later patch, those will be replaced with the respective includes.
    
    Signed-off-by: Georg Pfuetzenreuter <georg.pfuetzenreuter@suse.com>