undefine: Extend virsh undefine to support the new flag

undefine: Extend virsh undefine to support the new flag

If the domain has managed save image, and --managed-save is
not specified, then it fails with an error telling the user
that a managed save image still exists.

If the domain has managed save image, and --managed-save is
specified, it invokes virDomainUndefineFlags. If
virDomainUndefineFlags fails, then it tries to remove the managed
save image using virDomainManagedSaveRemove first, with
invoking virDomainUndefine following. (For compatibility between
new virsh with this patch and older libvirt without this patch).

Similarly if the domain has no managed save image. See the codes for
detail.

NOTE: Have not removing the codes checking if the domain is running
in function "cmdUndefine", it will go along with qemu driver's fix
(allow to undefine a running domain).