tests: qemuxml2xml: drop early file loading
tests: qemuxml2xml: drop early file loading

For the standard active/inactive XML testing, if we leave the file loading
up to the generic XML2XML infrastructure, we get the benefit of
VIR_TEST_REGENERATE_OUTPUT, at the price of a few more disk reads. Seems
worth it.

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