tests: qemuxml2argv: centralize CAPS suffix building
tests: qemuxml2argv: centralize CAPS suffix building

Reviewed-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>
Signed-off-by: Cole Robinson <7cd45ff6ad1fb7cf556a02797d774247851499f8@redhat.com>

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