[OVAL] xml export: fix 'set' element namespace creation
[OVAL] xml export: fix 'set' element namespace creation

Fixes #574069 - Output of OVAL "set" element only has namespace if AGGREGATE.

redhatrises/openscap,isimluk/openscap,jan-cerny/openscap,OpenSCAP/openscap,openprivacy/openscap,mpreisler/openscap,Hexadorsimal/openscap,ybznek/openscap,ybznek/openscap,ybznek/openscap,mpreisler/openscap,ybznek/openscap,redhatrises/openscap,jan-cerny/openscap,jan-cerny/openscap,isimluk/openscap,postfix/openscap,openprivacy/openscap,redhatrises/openscap,ybznek/openscap,postfix/openscap,OpenSCAP/openscap,redhatrises/openscap,postfix/openscap,isimluk/openscap,mpreisler/openscap,openprivacy/openscap,jan-cerny/openscap,Hexadorsimal/openscap,OpenSCAP/openscap,mpreisler/openscap,Hexadorsimal/openscap,isimluk/openscap,jan-cerny/openscap,postfix/openscap,postfix/openscap,OpenSCAP/openscap,OpenSCAP/openscap,mpreisler/openscap,OpenSCAP/openscap,Hexadorsimal/openscap,Hexadorsimal/openscap,redhatrises/openscap,mpreisler/openscap,jan-cerny/openscap,redhatrises/openscap,isimluk/openscap,postfix/openscap,openprivacy/openscap,openprivacy/openscap,Hexadorsimal/openscap,isimluk/openscap,openprivacy/openscap,ybznek/openscap