conf: Split out seclabel formating code for disk source
conf: Split out seclabel formating code for disk source

The code is common for all the various disk types. Split it out to a
common function.

VenkatDatta/libvirt,nertpinx/libvirt,VenkatDatta/libvirt,andreabolognani/libvirt,jardasgit/libvirt,jardasgit/libvirt,datto/libvirt,crobinso/libvirt,jfehlig/libvirt,nertpinx/libvirt,crobinso/libvirt,jfehlig/libvirt,jardasgit/libvirt,crobinso/libvirt,zippy2/libvirt,agx/libvirt,zippy2/libvirt,libvirt/libvirt,eskultety/libvirt,andreabolognani/libvirt,taget/libvirt,taget/libvirt,datto/libvirt,VenkatDatta/libvirt,VenkatDatta/libvirt,nertpinx/libvirt,crobinso/libvirt,jfehlig/libvirt,olafhering/libvirt,shugaoye/libvirt,libvirt/libvirt,shugaoye/libvirt,libvirt/libvirt,eskultety/libvirt,zippy2/libvirt,jardasgit/libvirt,shugaoye/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,zippy2/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,elmarco/libvirt,rlaager/libvirt,elmarco/libvirt,shugaoye/libvirt,rlaager/libvirt,datto/libvirt,jardasgit/libvirt,jfehlig/libvirt,elmarco/libvirt,rlaager/libvirt,shugaoye/libvirt,eskultety/libvirt,agx/libvirt,olafhering/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,libvirt/libvirt,agx/libvirt,elmarco/libvirt,olafhering/libvirt,taget/libvirt,datto/libvirt,nertpinx/libvirt,elmarco/libvirt,taget/libvirt,eskultety/libvirt,datto/libvirt,taget/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,agx/libvirt,rlaager/libvirt,agx/libvirt,andreabolognani/libvirt,rlaager/libvirt,eskultety/libvirt,olafhering/libvirt