SPEC: Use %license macro
    
    Starting with rpm 4.11, it is possible to install the license using
    a new file macro %license, this will separate the license files from documents
    and install them in a special directory in /usr/share
    
      rpm -q -l -p ./sssd-1.15.3-0.el7.x86_64.rpm
      /usr/share/licenses/sssd-1.15.3
      /usr/share/licenses/sssd-1.15.3/COPYING
    
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>