Add new fields to SR.stat: "clustered" and "health"
Add new fields to SR.stat: "clustered" and "health"

* Clustered implies that the SR uses aggregrated local storage, where "local"
  refers to the disks that are inside the XenServer hosts.
* The "health" field provides a way for the storage backend to signal to the
  toolstack whether the storage is currently degraded and being repaired in some
  way (e.g. by rebuilding RAID mirrors).

Signed-off-by: Rob Hoes <8783b3376fb07d39edffc8d7da68a6de3874a7e6@citrix.com>

xapi-project/message-switch,xapi-project/message-switch,xapi-project/message-switch