Ensure that util-linux-core is available
    
    In 1f3645b72d46a0a709878d786c9a4ec83c0e3a36 we added a removal of
    util-linux, so this section had both:
    
    %packages --excludedocs --instLangs=en --nocore --excludeWeakdeps
    util-linux
    ...
    -util-linux
    
    This changes the first of those two entries to include
    util-linux-core instead of util-linux, so these two directives do
    not conflict.
    
    Signed-off-by: Stephen Gallagher <sgallagh@redhat.com>