Fix release status generation post-oslo LP change

Release status page generation is broken since we renamed 'oslo' to
'oslo-incubator' in Launchpad. This fixes it.

This also removes oslo.messaging which is no longer tracked as part
of the Juno release (it has its separate release schedule).

Change-Id: I5cca639a7de2e05dd291ac93da4d67651575b065