api-ref: Rephrase delete volume precondition
Closes-Bug:
@@ -460,8 +460,9 @@ Deletes a volume.
Preconditions
-- Volume status must be ``available``, ``in-use``, ``error``, or
- ``error_restoring``.
+- Volume status must be ``available``, ``in-use``, ``error``,
+ ``error_restoring``, ``error_extending``, ``error_managing``,
+ and must not be migrating, attached, belong to a group or have snapshots.
- You cannot already have a snapshot of the volume.
