Fix reserve volume enforcing the wrong policy action

This PS fixes `reserve_volume` enforcing the wrong
policy action: retype policy. It has been corrected
to reserve volume policy. This is consistent with
the policy in code documentation as well for both
policies: retype is only enforced by os-retype and
reserve is only enforced by os-reserve [0][1]

[0] https://github.com/openstack/cinder/blob/94460b64fb06814e18a4459e365cf207b730210b/cinder/policies/volume_actions.py#L91
[1] https://github.com/openstack/cinder/blob/94460b64fb06814e18a4459e365cf207b730210b/cinder/policies/volume_actions.py#L197

Change-Id: I14b8288cdb066f30b66068dcaaf66e1277aa122f

cinder/volume/api.py

@@ -670,7 +670,7 @@ class API(base.Base):
         return snapshots
 
     def reserve_volume(self, context, volume):
-        context.authorize(vol_action_policy.RETYPE_POLICY, target_obj=volume)
+        context.authorize(vol_action_policy.RESERVE_POLICY, target_obj=volume)
         expected = {'multiattach': volume.multiattach,
                     'status': (('available', 'in-use') if volume.multiattach
                                else 'available')}

releasenotes/notes/fix-reserve-volume-policy-31790a8d865ee0a1.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    The reserve volume API was incorrectly enforcing "volume:retype" policy
+    action. It has been corrected to "volume_extension:volume_actions:reserve".