decouple oslo libs from integrated gate

This removes oslo libraries from the integrated gate, they will now be
tested at release versions by other projects, and have their own
forward testing jobs for their own changes to ensure their next
release doesn't break all of openstack.

We also have to decouple the large-ops jobs from the gate. Because we
have clean check, we can keep these check only, to prevent large
regressions in oslo.db and rootwrap, but not cogate all changes.

And remove some final pbr jobs that don't do what you'd think any
more, because they'd be only testing with released versions of
pbr. It's not clear why largeops, swift-functional, or cells were ever
added in the first place.

Change-Id: I92af1f40b1d8f86ca1573640913d73d831cc9b0e