This adds a config flag orders.window-endpoint-rollout-phase
that can take on the values phase1, phase2 or phase3.
In phase1, the current orders endpoint continues to work as
usual, and the windowed orders endpoint uses the same backend
as the current one (but also does a bit extra).
In phase2, the current orders endpoint is disabled and the
windowed orders endpoint continues to use the same backend.
In phase3, the current orders endpoint is still disabled and
the windowed orders endpoint uses the new backend that requires
much less database traffic and state.
The intention is to deploy in phase1, roll out code to nodes
to have them use the windowed endpoint, switch to phase2, wait
a couple days for all existing orders to expire, then switch
to phase3.
Additionally, it fixes a bug where a node could submit a bunch
of orders and rack up charges for a bucket.
Change-Id: Ifdc10e09ae1645159cbec7ace687dcb2d594c76d
