Upgrade of hardhandles does not set hippo:availability property correctly

The 'hardhandles' upgrade script does not set proper 'hippo:availability' values on the variants of a document.

In 7.8, the typical use case is one live variant with hippo:availability set to 'live' and 'preview'. The hardhandles script leaves it like that, and in addition creates a second 'unpublished' variant without any hippo:availibility property on it. That creates an incorrect state: the script should leave the published variant with 'hippo:availability' set to 'live', and the unpublished variant with 'hippo:availability' set to 'preview'.