This is not perfect as mypy at least doesn't consider e.g. subclasses of
the property decorator class to behave the same way, but it's as good as
we can get without introducing a mypy plugin.
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>
Change-Id: Ia0c4110218ce8a48c3ec5e720f07e45fc2b831bf