Make all relevancy expressions use comparison operators
    
    Rather than enumerating RHEL versions, use comparison against
    "known-good" version to make the expressions easier to read and
    understand.
    
    Also convert users of '~<' to '<', as '~<' compares only minor versions
    within the same major.
    
    Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>