This changeset includes some fixes to documentation discovered while working on
node pools, but we didn't want to include in the node pool PRs so they can get
backported easily:
* namespace apply/delete commands are forwarded to the authoritative region
* deleting a namespace requires there are no non-terminal jobs in any of the
federated regions
* fixed a typo in the name of the `nomad.client.allocated.disk` metric
Tim Gross