xenFormatXLDisk: Unify commas pattern for arguments
xenFormatXLDisk: Unify commas pattern for arguments

instead of:

  virBufferAdd(buf, "arg1,");
  virBufferAdd(buf, "arg2");

lets have:

  virBufferAdd(buf, "arg1");
  virBufferAdd(buf, ",arg2");

Because it's better. Consider we want to add conditionally arg3.
With this change, it's simple:

  if (cond)
    virBufferAdd(buf, ",arg3");

with current code there might be a comma hanging at EOL.

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>

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