storagePoolDefineXML: prefer using newDef to save config file
storagePoolDefineXML: prefer using newDef to save config file

When re-defining an active storage pool, due to a bug the config
file on disk is not changed. This is because we are passing old
definition instead of new one to virStoragePoolObjSaveDef.
This issue was introduced by bfcd8fc9,

Signed-off-by: Changkuo Shi <74456bc9ef3449c593e9c11e20867960b1d7eaa1@h3c.com>
Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>

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