Formally deprecate the allow_port_security_disabled feature flag

Now that Liberty is EOL, the feature flag is not needed anymore. But
we still need to deprecate it in order to remove it later.

Change-Id: If0b2168080a0b0ecdc6682ef69856a0879f4f6d3
diff --git a/releasenotes/notes/deprecate-allow_port_security_disabled-option-2d3d87f6bd11d03a.yaml b/releasenotes/notes/deprecate-allow_port_security_disabled-option-2d3d87f6bd11d03a.yaml
new file mode 100644
index 0000000..4acdc6d
--- /dev/null
+++ b/releasenotes/notes/deprecate-allow_port_security_disabled-option-2d3d87f6bd11d03a.yaml
@@ -0,0 +1,8 @@
+---
+upgrade:
+  - The default value for the ``allow_port_security_disabled`` option in the
+    ``compute-feature-enabled`` section has been changed from ``False``
+    to ``True``.
+deprecations:
+  - The ``allow_port_security_disabled`` option in the
+   ``compute-feature-enabled`` section is now deprecated.
diff --git a/tempest/config.py b/tempest/config.py
index 0e45f2e..ba100a8 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -329,9 +329,12 @@
     # NOTE(mriedem): This is a feature toggle for bug 1175464 which is fixed in
     # mitaka and newton. This option can be removed after liberty-eol.
     cfg.BoolOpt('allow_port_security_disabled',
-                default=False,
+                default=True,
                 help='Does the test environment support creating ports in a '
-                     'network where port security is disabled?'),
+                     'network where port security is disabled?',
+                deprecated_for_removal=True,
+                deprecated_reason='This config switch was added for Liberty '
+                                  'which is not supported anymore.'),
     cfg.BoolOpt('disk_config',
                 default=True,
                 help="If false, skip disk config tests"),