rose app-upgrade: fix trigger.

This fixes a typo that led to the post-upgrade
triggers being based on the old metadata, not
the post-upgrade metadata.

The existing test-battery did not do a good
job of capturing the post-upgrade triggering
(as it did not catch this bug) so it has
been improved.
Merge pull request #1132 from benfitzpatrick/rose-app-upgrade.fix-trigger

rose app-upgrade: fix post-upgrade trigger metadata