It is currently possible to rename or unset the availability_zone
metadata value on a host aggregate which can adversely impact
instances that were created in that specific AZ since later
attempts to migrate or unshelve those instances will fail if the
AZ with the original name no longer exists.
This adds a warning to the API reference for updating the AZ
name and also fixes a grammar typo in the 'metadata' response
parameter description.
Change-Id: Ie9d4a1ff1a23827490fe51350c11292c6efc4eb2
Related-Bug: #1378904
Matt Riedemann
5dc1ed3c5c