conf: use virXMLPropString and virXMLNodeContentString for vcpu parsing
conf: use virXMLPropString and virXMLNodeContentString for vcpu parsing

XPath is good for random search of elements, not for accessing
attributes of one node.

Signed-off-by: Pavel Hrdina <d4772d05997b8abf035041e3b4f4996380ea7e7a@redhat.com>

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