Automatic merge from submit-queue
AWS/GCE: Spread PetSet volume creation across zones, create GCE volumes in non-master zones
Long term we plan on integrating this into the scheduler, but in the
short term we use the volume name to place it onto a zone.
We hash the volume name so we don't bias to the first few zones.
If the volume name "looks like" a PetSet volume name (ending with
-<number>) then we use the number as an offset. In that case we hash
the base name.
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