Update admin guide on handling drive failures

Simply replacing a failed disk requires a very long time if the ring is not
changed, because all data will be replicated to a single new disk. This extends
the time to recover from missing replicas, and becomes even more important with
bigger disks.

This patch updates the doc to include a faster alternative by setting the weight
of a failed disk to 0.  In this case the partitions from the failed disk are
distributed and replicated to the remaining disks in the cluster, and because
each disk gets only a fraction of the partitions it's also much faster.

Change-Id: I16617756359771ad89ca5d4690b58a014f481d9b
Return 403 on unauthorized upload when over account quota

If you try an unauthorized upload into a container that is over quota you get
a 403 instead of a 413, but if you try to unauthorized upload when an
*account* is over quota you can see the 413 even though the upload would have
been rejected by the authorize callback.  By wrapping the authorize callback
associated with the incoming request we can make sure to only return our 413
when the request would have been authorized otherwise.

Drive by doc fixes thanks to acoles:

 * State that container_quotas should be after auth middleware in
   the class doc string.
 * Add note to proxy-server.conf.sample that account_quotas should
   be after auth middleware.

The equivalent statements are already in place for each quota
middleware.

Doc-Impact

Closes-Bug: #1387415
Change-Id: I2a88b3ec79d35bfdd73ea6ad64e376b7c7af4ea6
Merge "Update admin guide on handling drive failures"