Use pandoc-common instead of python3-kickstart for package tests
    
    Reasoning:
    
    1. pandoc is not in critpath so will not itself be tested
    2. pandoc is widely used and actively maintained
    3. package is noarch
    4. package has minimal deps
    
    Hopefully this will work for everything. For some reason, the
    "use python3-blivet for pykickstart tests" fails mysteriously
    sometimes, see e.g.
    https://openqa.stg.fedoraproject.org/tests/2672282
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>