virfile: Add error for root squash change mode failure
virfile: Add error for root squash change mode failure

This will only be seen when debugging, but in order to help determine
whether a virFileOpenForceOwnerMode failed during an NFS root-squash
volume/file creation, add an error message from the child.

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