Convert license to SPDX format
    
    Note the BSD-2-Clause and GPL-2.0-or-later references are from lenses
    whose license is unclear. This is reported upstream at
    
      https://github.com/hercules-team/augeas/issues/816
    
    where BSD-2-Clause was suggested and confirmed by the author. The
    GPL-2.0-or-later was picked for the unspecified GPL version based
    on discussion at:
    
      https://lists.fedoraproject.org/archives/list/legal@lists.fedoraproject.org/thread/WMN4OKQOQLCKMRMIHOJ5XHJAT4QEF5LY/
    
    Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>