Fix creation of protected image for old user code

Commit afb4969 [1][2] replaced "protected" with "is_protected" in
raw image properties in order to fix an server-side schema validation
error (400 Bad Request) when defining image properties. That change
broke user code which calls e.g. create_image() with "protected"
instead of "is_protected" causing the exact server-side schema
validation error which it tried to fix for "is_protected" [3].

This patch readds "protected" to raw image properties and thus allows
clients to continue to use the old "protected" attribute.

Ref.:
[1] afb4969
[2] https://review.opendev.org/c/openstack/openstacksdk/+/820926
[3] https://bugs.launchpad.net/python-glanceclient/+bug/1927215

Change-Id: I37b046dd71c29734504cf55f272b6dffbb8b2aad

Author: JM1

openstack/image/v2/_proxy.py

@@ -26,7 +26,7 @@
 # Rackspace returns this for intermittent import errors
 _IMAGE_ERROR_396 = "Image cannot be imported. Error code: '396'"
 _INT_PROPERTIES = ('min_disk', 'min_ram', 'size', 'virtual_size')
-_RAW_PROPERTIES = ('is_protected', 'tags')
+_RAW_PROPERTIES = ('is_protected', 'protected', 'tags')
 
 
 class Proxy(_base_proxy.BaseImageProxy):