Add k-var-headers Obsoletes/Provides
    
    When doing a variant build, you want kernel-variant-headers to Obsoletes:
    and Provides: kernel-headers, so that it can upgrade/replace
    kernel-headers. Otherwise, attempting to install kernel-variant-headers
    leads to rpm spewing file conflicts with kernel-headers, if installed.
    
    Signed-off-by: Jarod Wilson <jarod@redhat.com>