When creating Openstack VMs the user has to specify the image it wants
to use. sstream-mirror-glance adds a date to the image name, so they
always have to recheck which is the current latest image.
This commit tests the usage of the `set_latest_property` configuration.
When --set-latest-property is given sstream-mirror-glance will set the
recently synced image with the `latest=true` property and then remove
the `latest` property from all the os_version/architecture matching
images.
Closes-bug: LP #1933130
98faf67846