virsh: Create macro for "overwrite" and no-overwrite" options
virsh: Create macro for "overwrite" and no-overwrite" options

Although not currently used in more than one command, it soon will be
so create a common macro to be used in the new command location.

Additionally, add the ".flags = 0," for both to match the expections
of the structure being predefined.

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