qemu: Refactor disk source string formatting
qemu: Refactor disk source string formatting

This patch adds function qemuGetDriveSourceString to produce
qemu-compatible disk source strings that will enable to reuse the code
and refactors building of the qemu commandline of disks to use this new
helper.

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