Drop AvailabilityZoneFilter inline with upstream removal

The was removed from upstream nova in the 2023.2 cycle
via commit 5edd805fe2395f35ecdfe5b589a51dc00565852f.

The nova release note states:

The ``AvailabilityZoneFilter`` was deprecated for removal
in 24.0.0 (Xena) and has now been removed.
The functionality of the``AvailabilityZoneFilter`` has been
replaced by the``map_az_to_placement_aggregate`` pre-filter.
The  pre-filter was introduced in 18.0.0 (Rocky) and enabled
by default in 24.0.0 (Xena). This pre-filter is now always
enabled and the ``[scheduler] query_placement_for_availability_zone``
config option has been removed.

This change also syncs the charm-helpers change from:
https://github.com/juju/charm-helpers/pull/850

Closes-Bug: #2037751
Closes-Bug: #2036766
Change-Id: I315900a7e32ec66b27fa69961e9b7dcb9fa1f949

charmhelpers/contrib/openstack/utils.py

@@ -585,7 +585,6 @@ def get_installed_os_version():
     return openstack_release().get('OPENSTACK_CODENAME')
 
 
-@cached
 def openstack_release():
     """Return /etc/os-release in a dict."""
     d = {}

hooks/nova_cc_context.py

@@ -381,6 +381,15 @@ _victoria_enabled_filters = [
     "DifferentHostFilter",
     "SameHostFilter",
 ]
+_bobcat_enabled_filters = [
+    "ComputeFilter",
+    "ComputeCapabilitiesFilter",
+    "ImagePropertiesFilter",
+    "ServerGroupAntiAffinityFilter",
+    "ServerGroupAffinityFilter",
+    "DifferentHostFilter",
+    "SameHostFilter",
+]
 
 
 def default_enabled_filters():
@@ -392,6 +401,8 @@ def default_enabled_filters():
     """
     os_rel = ch_utils.os_release('nova-common')
     cmp_os_rel = ch_utils.CompareOpenStackReleases(os_rel)
+    if cmp_os_rel >= 'bobcat':
+        return _bobcat_enabled_filters
     if cmp_os_rel >= 'victoria':
         return _victoria_enabled_filters
     if cmp_os_rel >= 'pike':

unit_tests/test_nova_cc_contexts.py

@@ -738,3 +738,8 @@ class NovaComputeContextTests(CharmTestCase):
         self.os_release.return_value = 'victoria'
         self.assertEqual(context.default_enabled_filters(),
                          context._victoria_enabled_filters)
+
+    def test_default_enabled_filters_bobcat(self):
+        self.os_release.return_value = 'bobcat'
+        self.assertEqual(context.default_enabled_filters(),
+                         context._bobcat_enabled_filters)