[all][requirements] requirements branched train - cycle-trailing are on notice that master is now ussuri

Just a friendly ping that the train keeps rolling.

Master is now ussuri. https://releases.openstack.org/constraints/upper/ussuri should work soon for those that want to switch their install_command in tox.ini within master earlier in the cycle (rather than having things pile up). I'll email again once it's working.

cycle-trailing projects are on notice that if they track master, the dependencies may change from what they are currently working on (train).

If you have any questions please let me know (in the #openstack-requirements channel preferably).

P.S. FFE season is over