Allow building this package during Python bootstrap
    
    This package needs to be available when Python is built for the second time,
    because it is required by systemtap.
    Hence it needs to be built before the tests and doc dependencies are ready
    and before Python gains the requirement on python3-rpm-generators.
    
    * Add a tests bcond.
    * Add a doc bcond.
    * Add a manual BuildRequires on python3-rpm-generators.
    
    [skip changelog]