tests: Pass BlockIOThrottle arguments by reference not value
tests: Pass BlockIOThrottle arguments by reference not value

Pass the data by reference rather than everything on the stack.

Signed-off-by: John Ferlan <87558058f6f829e5ec976c8ef960720af4ff9c7d@redhat.com>

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