Fix AZ related API docs
While we have a big fat comment in the development docs explaining why it's so
terrible to use default AZ values for either booting an instance or setting
an aggregate AZ metadata, we still have confusing API docs that provide the
wrong name for the AZ...
Fixing that and trying to explain the problem within the docs, too.
This reverts commit 92ca21abd61b6df7fc8bc5ffe7502f03b3eca2dd.
Co-Authored-By: Sylvain Bauza <sbauza@redhat.com>
Co-Authored-By: Stephen Finucane <stephenfin@redhat.com>
Change-Id: Ie4bfe32bbef0f8060bfc0ad4190f262d4a8bd3b2
d2c8d41878