The new helper replaces the 'value' part of the key-value tuple in an
object. The advantage of this new helper is that it preserves the
ordering of the key in the object when compared to a combination of
stealing the old key and adding a new value. This will be needed for a
new test/helper for validating and modifying qemu capabilities data.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com>