When handling the "pet" case, some nodes may be critical for the deployment.
For example, in an OpenStack installer like TripleO you may want to make
sure your controllers are not removed by an incorrect operation.
This changes introduces a new field "protected" on nodes. When it is
set to True, the "deleted" and "rebuild" provisioning actions fail with
HTTP 403. Deleting such nodes is also not possible.
Also adds "protected_reason" for the operators to specify the reason
a node is protected.
Story: #2003869
Task: #26706
Change-Id: I1950bf6dd65b6596cae69d431ef288e578a89d6e
68d62f2bee